locks: Add ofd locks c/r

OFD locks logic reuses existing locks c/r functionality.

https://github.com/xemul/criu/issues/42


travis-ci: success for series starting with [1/2] locks: Add ofd locks c/r
Signed-off-by: Begunkov Pavel <asml.silence@gmail.com>
Signed-off-by: Eugene Batalov <eabatalov89@gmail.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>