locking: store the write time in the locking.tdb

locking: store the write time in the locking.tdb

This is needed to implement the strange write time update
logic later. We need to store 2 time timestamps to
distinguish between the time the file system had before
the first client opened the file and a forced timestamp update.

metze
(This used to be commit 6aaa2ce0eeb46f6735ec984a2e7aadde7a7f456d)