nfsd: keep a tally of RECLAIM_COMPLETE operations when using nfsdcld

When using nfsdcld for NFSv4 client tracking, track the number of
RECLAIM_COMPLETE operations we receive from "known" clients to help in
deciding if we can lift the grace period early (or whether we need to
start a v4 grace period at all).

Signed-off-by: Scott Mayhew <smayhew@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>