GFS2: smbd proccess hangs with flock() call.

GFS2 currently does not support mandatory flocks. An flock() call with
LOCK_MAND triggers unexpected behavior because gfs2 is not checking for
this lock type. This patch corrects that.

Signed-off-by: Abhi Das <adas@redhat.com>
Signed-off-by: Steven Whitehouse <swhiteho@redhat.com>