SUNRPC: Deprecate support for site-local addresses

RFC 3879 "formally deprecates" site-local IPv6 addresses.  We
interpret that to mean that the scope ID is ignored for all but
link-local addresses.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Acked-by: Jeff Layton <jlayton@redhat.com>
Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>