Mark functions as static

Mark functions used only in the same translation unit as static. This
only includes functions that do not have a prototype in a header file
either.

Reviewed-by: Ryan Moeller <ryan@iXsystems.com>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Arvind Sankar <nivedita@alum.mit.edu>
Closes #10470

module/zfs/dsl_dir.c

@@ -1684,7 +1684,7 @@ dsl_dir_set_quota(const char *ddname, zprop_source_t source, uint64_t quota)
 	    ZFS_SPACE_CHECK_EXTRA_RESERVED));
 }
 
-int
+static int
 dsl_dir_set_reservation_check(void *arg, dmu_tx_t *tx)
 {
 	dsl_dir_set_qr_arg_t *ddsqra = arg;