dm: Fix dm_accept_partial_bio() relative to zone management commands

dm: Fix dm_accept_partial_bio() relative to zone management commands

[ Upstream commit 6842d264aa5205da338b6dcc6acfa2a6732558f1 ]

Fix dm_accept_partial_bio() to actually check that zone management
commands are not passed as explained in the function documentation
comment. Also, since a zone append operation cannot be split, add
REQ_OP_ZONE_APPEND as a forbidden command.

White lines are added around the group of BUG_ON() calls to make the
code more legible.

Signed-off-by: Damien Le Moal <damien.lemoal@wdc.com>
Signed-off-by: Mike Snitzer <snitzer@redhat.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>