Remote and local adv lock servers might de-synchronize (the added comment
explains the plausible scenario), resulting in EDEADLK returned on the
local registration attempt. Handle this by re-trying the local op [1].

On unmount, local registration abort is indicated as EINTR, abort the nlm
call as well.

Reported and tested by: pho
Suggested and reviewed by: dfr (previous version, [1])
Sponsored by: The FreeBSD Foundation
MFC after: 1 week
Approved by: re (delphij)