block: Don't merge requests if integrity flags differ

We'd occasionally merge requests with conflicting integrity flags.
Introduce a merge helper which checks that the requests have compatible
integrity payloads.

Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Jens Axboe <axboe@fb.com>

diff --cc block/blk-integrity.c
Simple merge

diff --cc block/blk-merge.c
Simple merge

diff --cc include/linux/blkdev.h
Simple merge