zdb: show bp in uberblock dump

Just another useful nugget of info in times of strife.

Sponsored-by: https://despairlabs.com/sponsor/
Reviewed-by: George Melikov <mail@gmelikov.ru>
Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Signed-off-by: Rob Norris <robn@despairlabs.com>
Closes openzfs#16667

cmd/zdb/zdb.c

@@ -4266,6 +4266,10 @@ dump_uberblock(uberblock_t *ub, const char *header, const char *footer)
 	(void) printf("\ttimestamp = %llu UTC = %s",
 	    (u_longlong_t)ub->ub_timestamp, ctime(&timestamp));
 
+	char blkbuf[BP_SPRINTF_LEN];
+	snprintf_blkptr(blkbuf, sizeof (blkbuf), &ub->ub_rootbp);
+	(void) printf("\tbp = %s\n", blkbuf);
+
 	(void) printf("\tmmp_magic = %016llx\n",
 	    (u_longlong_t)ub->ub_mmp_magic);
 	if (MMP_VALID(ub)) {