nfsd: handle legacy client tracking records sent by nfsdcld

The new nfsdcld will do a one-time "upgrade" where it searches for
records from nfsdcltrack and the legacy tracking during startup.
Legacy records will be prefixed with the string "hash:", which we need
to strip off before adding to the reclaim_str_hashtbl.  When legacy
records are encountered, set the new cn_has_legacy flag in the cld_net.
When this flag is set, if the search for a reclaim record based on the
client name string fails, then do a second search based on the hash of
the name string.

Note that if there are legacy records then the grace period will not
be lifted early via the tracking of RECLAIM_COMPLETEs.

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