block: Refuse request/bio merges with gaps in the integrity payload

If a driver sets the block queue virtual boundary mask, it means that
it cannot handle gaps so we must not allow those in the integrity
payload as well.

Signed-off-by: Sagi Grimberg <sagig@mellanox.com>

Fixed up by me to have duplicate integrity merge functions, depending
on whether block integrity is enabled or not. Fixes a compilations
issue with CONFIG_BLK_DEV_INTEGRITY unset.

Signed-off-by: Jens Axboe <axboe@fb.com>
diff --git a/block/blk-integrity.c b/block/blk-integrity.c
index f548b64..75f29cf 100644
--- a/block/blk-integrity.c
+++ b/block/blk-integrity.c
@@ -204,6 +204,9 @@
 	    q->limits.max_integrity_segments)
 		return false;
 
+	if (integrity_req_gap_back_merge(req, next->bio))
+		return false;
+
 	return true;
 }
 EXPORT_SYMBOL(blk_integrity_merge_rq);