Cleanup: Specify unsignedness on things that should not be signed

In #13871, zfs_vdev_aggregation_limit_non_rotating and
zfs_vdev_aggregation_limit being signed was pointed out as a possible
reason not to eliminate an unnecessary MAX(unsigned, 0) since the
unsigned value was assigned from them.

There is no reason for these module parameters to be signed and upon
inspection, it was found that there are a number of other module
parameters that are signed, but should not be, so we make them unsigned.
Making them unsigned made it clear that some other variables in the code
should also be unsigned, so we also make those unsigned. This prevents
users from setting negative values that could potentially cause bad
behaviors. It also makes the code slightly easier to understand.

Mostly module parameters that deal with timeouts, limits, bitshifts and
percentages are made unsigned by this. Any that are boolean are left
signed, since whether booleans should be considered signed or unsigned
does not matter.

Making zfs_arc_lotsfree_percent unsigned caused a
`zfs_arc_lotsfree_percent >= 0` check to become redundant, so it was
removed. Removing the check was also necessary to prevent a compiler
error from -Werror=type-limits.

Several end of line comments had to be moved to their own lines because
replacing int with uint_t caused us to exceed the 80 character limit
enforced by cstyle.pl.

The following were kept signed because they are passed to
taskq_create(), which expects signed values and modifying the
OpenSolaris/Illumos DDI is out of scope of this patch:

	* metaslab_load_pct
	* zfs_sync_taskq_batch_pct
	* zfs_zil_clean_taskq_nthr_pct
	* zfs_zil_clean_taskq_minalloc
	* zfs_zil_clean_taskq_maxalloc
	* zfs_arc_prune_task_threads

Also, negative values in those parameters was found to be harmless.

The following were left signed because either negative values make
sense, or more analysis was needed to determine whether negative values
should be disallowed:

	* zfs_metaslab_switch_threshold
	* zfs_pd_bytes_max
	* zfs_livelist_min_percent_shared

zfs_multihost_history was made static to be consistent with other
parameters.

A number of module parameters were marked as signed, but in reality
referenced unsigned variables. upgrade_errlog_limit is one of the
numerous examples. In the case of zfs_vdev_async_read_max_active, it was
already uint32_t, but zdb had an extern int declaration for it.

Interestingly, the documentation in zfs.4 was right for
upgrade_errlog_limit despite the module parameter being wrongly marked,
while the documentation for zfs_vdev_async_read_max_active (and friends)
was wrong. It was also wrong for zstd_abort_size, which was unsigned,
but was documented as signed.

Also, the documentation in zfs.4 incorrectly described the following
parameters as ulong when they were int:

	* zfs_arc_meta_adjust_restarts
	* zfs_override_estimate_recordsize

They are now uint_t as of this patch and thus the man page has been
updated to describe them as uint.

dbuf_state_index was left alone since it does nothing and perhaps should
be removed in another patch.

If any module parameters were missed, they were not found by `grep -r
'ZFS_MODULE_PARAM' | grep ', INT'`. I did find a few that grep missed,
but only because they were in files that had hits.

This patch intentionally did not attempt to address whether some of
these module parameters should be elevated to 64-bit parameters, because
the length of a long on 32-bit is 32-bit.

Lastly, it was pointed out during review that uint_t is a better match
for these variables than uint32_t because FreeBSD kernel parameter
definitions are designed for uint_t, whose bit width can change in
future memory models.  As a result, we change the existing parameters
that are uint32_t to use uint_t.

Reviewed-by: Alexander Motin <mav@FreeBSD.org>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Neal Gompa <ngompa@datto.com>
Signed-off-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Closes #13875

cmd/zdb/zdb.c

@@ -117,10 +117,10 @@ zdb_ot_name(dmu_object_type_t type)
 extern int reference_tracking_enable;
 extern int zfs_recover;
 extern unsigned long zfs_arc_meta_min, zfs_arc_meta_limit;
-extern int zfs_vdev_async_read_max_active;
+extern uint_t zfs_vdev_async_read_max_active;
 extern boolean_t spa_load_verify_dryrun;
 extern boolean_t spa_mode_readable_spacemaps;
-extern int zfs_reconstruct_indirect_combinations_max;
+extern uint_t zfs_reconstruct_indirect_combinations_max;
 extern uint_t zfs_btree_verify_intensity;
 
 static const char cmdname[] = "zdb";

cmd/ztest.c

@@ -253,10 +253,10 @@ static const ztest_shared_opts_t ztest_opts_defaults = {
 extern uint64_t metaslab_force_ganging;
 extern uint64_t metaslab_df_alloc_threshold;
 extern unsigned long zfs_deadman_synctime_ms;
-extern int metaslab_preload_limit;
+extern uint_t metaslab_preload_limit;
 extern int zfs_compressed_arc_enabled;
 extern int zfs_abd_scatter_enabled;
-extern int dmu_object_alloc_chunk_shift;
+extern uint_t dmu_object_alloc_chunk_shift;
 extern boolean_t zfs_force_some_double_word_sm_entries;
 extern unsigned long zio_decompress_fail_fraction;
 extern unsigned long zfs_reconstruct_indirect_damage_fraction;
@@ -4639,7 +4639,7 @@ ztest_dmu_object_next_chunk(ztest_ds_t *zd, uint64_t id)
 {
 	(void) id;
 	objset_t *os = zd->zd_os;
-	int dnodes_per_chunk = 1 << dmu_object_alloc_chunk_shift;
+	uint_t dnodes_per_chunk = 1 << dmu_object_alloc_chunk_shift;
 	uint64_t object;
 
 	/*