mdserver_remote: fill in OffsetFromServer method
mdserver_remote: fill in OffsetFromServer method

Issue: KBFS-1312

keybase/client,keybase/client,keybase/kbfs,keybase/client,keybase/kbfs,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/client,keybase/kbfs,keybase/kbfs,keybase/client,keybase/client