lockd: Adjust nlmclnt_lookup_host() signature to accomodate non-AF_INET

Pass a struct sockaddr * and a length to nlmclnt_lookup_host() to
accomodate non-AF_INET family addresses.

As a side benefit, eliminate the hostname_len argument, as the hostname
is always NUL-terminated.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: J. Bruce Fields <bfields@citi.umich.edu>