NFSv4: increase client-provided nfs4 clientid size

Neil Brown observed that the current limit of 32 bytes isn't enough to hold two
ip addresses and the rest of the stuff we're putting in it, so it's often
truncated to the point where it's unlikely to be unique.  This can cause
spurious CLID_INUSE's from the server.

Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>
(cherry picked from fc8c17ec251e984ab3df9182ed097aa5b577c915 commit)