locks: allow lockd to process blocked locks during grace period

The check here is currently harmless but unnecessary, since, as the
comment notes, there aren't any blocked-lock callbacks to process
during the grace period anyway.

And eventually we want to allow multiple grace periods that come and go
for different filesystems over the course of the lifetime of lockd, at
which point this check is just going to get in the way.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>