filelock: fix deadlock detection in POSIX locking

filelock: fix deadlock detection in POSIX locking

The FL_POSIX check in __locks_insert_block was inadvertantly broken
recently and is now inserting only OFD locks instead of only legacy
POSIX locks.

This breaks deadlock detection in POSIX locks, and may also be the root
cause of a performance regression noted by the kernel test robot.
Restore the proper sense of the test.

Fixes: b6be3714005c ("filelock: convert __locks_insert_block, conflict and deadlock checks to use file_lock_core")
Reported-by: kernel test robot <oliver.sang@intel.com>
Closes: https://lore.kernel.org/oe-lkp/202402181229.f8147f40-oliver.sang@intel.com
Signed-off-by: Jeff Layton <jlayton@kernel.org>
Link: https://lore.kernel.org/r/20240218-flsplit4-v1-1-26454fc090f2@kernel.org
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Christian Brauner <brauner@kernel.org>