s3: locking: Convert on the wire behavior of POSIX (UNIX extensions) locks from proce...

s3: locking: Convert on the wire behavior of POSIX (UNIX extensions) locks from process-associated locks to open file description locks.

This means locks are associated with the SMB handle
they were created on, not the inode. In all other ways
they behave like UNIX extensions fcntl (process-associated)
locks. Torture test to follow.

When a handle is closed all locks attached to that handle
are closed, not all locks on the underlying inode. In
this respect they now behave like Windows locks.

The key to this in the UNIX extensions locking codepath is modifying
the reference count only when a new locking context is seen
on any lock request, and decrementing the reference count
when the last instance of a locking context is seen on any
unlock request. For SMB2+ the persistent part of a file handle
is used as the locking context so this behavior becomes
natural.

This is a behavior change but after consultation with
Jeff Layton and Steve French the only client that implements
UNIX extensions POSIX locks - the cifsfs client - already
expects these locks to behave like open file description
(ofd) locks. With our previous behavior Linux ofd-locks
fail against smbd.

Signed-off-by: Jeremy Allison <jra@samba.org>
Reviewed-by: Jeff Layton <jlayton@samba.org>