ocfs2_dlm: Make dlmunlock() wait for migration to complete

dlmunlock() was not waiting for migration to complete before releasing locks
on locally mastered locks.

Signed-off-by: Kurt Hackel <kurt.hackel@oracle.com>
Signed-off-by: Sunil Mushran <Sunil.Mushran@oracle.com>
Signed-off-by: Mark Fasheh <mark.fasheh@oracle.com>