test/zdtm/static: split ofd_file_locks.h to .c/.h

Having a "header library" is nice if it's small and clean, but
 - we compile its code a few times;
 - there is no distinction between internal and external functions.

Let's separate functions out of header and into a .c file.

Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>