Report dnodes with faulty bonuslen

In files created/modified before 4254acb there may be a corruption of
xattrs which is not reported during scrub and normal send/receive. It
manifests only as an error when raw sending/receiving. This happens
because currently only the raw receive path checks for discrepancies
between the dnode bonus length and the spill pointer flag.

In case we encounter a dnode whose bonus length is greater than the
predicted one, we should report an error. Modify in this regard
dnode_sync() with an assertion at the end, dump_dnode() to error out,
dsl_scan_recurse() to report errors during a scrub, and zstream to
report a warning when dumping. Also added a test to verify spill blocks
are sent correctly in a raw send.

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: George Amanakis <gamanakis@gmail.com>
Closes #12720 
Closes #13014

module/zfs/dnode_sync.c

@@ -854,6 +854,8 @@ dnode_sync(dnode_t *dn, dmu_tx_t *tx)
 		dnode_rele(dn, (void *)(uintptr_t)tx->tx_txg);
 	}
 
+	ASSERT3U(dnp->dn_bonuslen, <=, DN_MAX_BONUS_LEN(dnp));
+
 	/*
 	 * Although we have dropped our reference to the dnode, it
 	 * can't be evicted until its written, and we haven't yet