block: bypass the STABLE_WRITES flag for protection information

block: bypass the STABLE_WRITES flag for protection information

Currently registering a checksum-enabled (aka PI) integrity profile sets
the QUEUE_FLAG_STABLE_WRITE flag, and unregistering it clears the flag.
This can incorrectly clear the flag when the driver requires stable
writes even without PI, e.g. in case of iSCSI or NVMe/TCP with data
digest enabled.

Fix this by looking at the csum_type directly in bdev_stable_writes and
not setting the queue flag.  Also remove the blk_queue_stable_writes
helper as the only user in nvme wants to only look at the actual
QUEUE_FLAG_STABLE_WRITE flag as it inherits the integrity configuration
by other means.

Signed-off-by: Christoph Hellwig <hch@lst.de>