fs: dlm: make F_SETLK use unkillable wait_event

While a non-waiting posix lock request (F_SETLK) is waiting for
user space processing (in dlm_controld), wait for that processing
to complete with an unkillable wait_event(). This makes F_SETLK
behave the same way for F_RDLCK, F_WRLCK and F_UNLCK. F_SETLKW
continues to use wait_event_killable().

Cc: stable@vger.kernel.org
Signed-off-by: Alexander Aring <aahringo@redhat.com>
Signed-off-by: David Teigland <teigland@redhat.com>