OpenZFS 9454 - ::zfs_blkstats should count embedded blocks

When we do a scrub or resilver, ZFS counts the different types of blocks,
which can be printed by the ::zfs_blkstats mdb dcmd. However, it fails to
count embedded blocks.

Porting notes:
* Commit d4a72f2 moved count_blocks under a BP_IS_EMBEDDED conditional
  as part of the sequential resilver functionality.  Since phys_birth
  would be zero that case should never happen as described above.  This
  is confirmed by the code coverage analysis.  Remove the conditional
  to realign that aspect of this function with OpenZFS.

Authored by: Matthew Ahrens <[email protected]>
Reviewed by: Dan Kimmel <[email protected]>
Reviewed by: George Wilson <[email protected]>
Reviewed by: George Melikov <[email protected]>
Reviewed by: Tom Caputi <[email protected]>
Ported-by: Brian Behlendorf <[email protected]>
Approved by: Robert Mustacchi <[email protected]>

OpenZFS-issue: https://www.illumos.org/issues/9454
OpenZFS-commit: openzfs/openzfs@d8a447a7
Closes #7697

module/zfs/dsl_scan.c

@@ -3565,14 +3565,14 @@ dsl_scan_scrub_cb(dsl_pool_t *dp,
 	boolean_t needs_io = B_FALSE;
 	int zio_flags = ZIO_FLAG_SCAN_THREAD | ZIO_FLAG_RAW | ZIO_FLAG_CANFAIL;
 
+	count_block(scn, dp->dp_blkstats, bp);
+
 	if (phys_birth <= scn->scn_phys.scn_min_txg ||
 	    phys_birth >= scn->scn_phys.scn_max_txg)
 		return (0);
 
-	if (BP_IS_EMBEDDED(bp)) {
-		count_block(scn, dp->dp_blkstats, bp);
-		return (0);
-	}
+	/* Embedded BP's have phys_birth==0, so we reject them above. */
+	ASSERT(!BP_IS_EMBEDDED(bp));
 
 	ASSERT(DSL_SCAN_IS_SCRUB_RESILVER(scn));
 	if (scn->scn_phys.scn_func == POOL_SCAN_SCRUB) {