lockd: Use sockaddr_storage for h_saddr field

To store larger addresses in the nlm_host structure, make h_saddr a
sockaddr_storage.  And let's call it something more self-explanatory:
"saddr" could easily be mistaken for "server address".

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