Introduce a version of nfs_get_mount_client() that supports AF_INET6 and
AF_INET server addresses. If the TI-RPC library is not available when
the showmount command is built, fall back to the legacy RPC user-space
API.
Signed-off-by: Chuck Lever <chuck.lever@oracle.com> Signed-off-by: Steve Dickson <steved@redhat.com>