CIFS: Add cifs_set_oplock_level

Simplify many places when we need to set oplock level on an inode.

Signed-off-by: Pavel Shilovsky <piastryyy@gmail.com>
Reviewed-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Steve French <sfrench@us.ibm.com>

diff --cc fs/cifs/cifsproto.h
Simple merge

diff --cc fs/cifs/file.c
Simple merge

diff --cc fs/cifs/misc.c
Simple merge