apparmor: use per file locks for transactional queries

As made mention of in commit 1dea3b41 ("apparmor: speed up
transactional queries"), a single lock is currently used to synchronize
transactional queries. We can, use the lock allocated for each file by
VFS instead.

Signed-off-by: Hamza Mahfooz <someguy@effective-light.com>
Signed-off-by: John Johansen <john.johansen@canonical.com>