nfsd: set timeparms.to_maxval in setup_callback_client

commit 3758cf7e14b753838fe754ede3862af10b35fdac upstream.

...otherwise the logic in the timeout handling doesn't work correctly.

Spotted-by: Trond Myklebust <trond.myklebust@primarydata.com>
Signed-off-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: J. Bruce Fields <bfields@redhat.com>
[bwh: Backported to 3.2: max_cb_time() takes no parameters]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>