There are three helpers that convert sockaddr-style addresses to text

addresses, then construct mount options to pass these addresses to the
kernel.  The tail of each of these helpers does exactly the same thing,
so introduce a helper that handles the common code.

Magically, the new helper supports IPv6 as well as IPv4.

Signed-off-by: Chuck Lever <chuck.lever@oracle.com>
Signed-off-by: Steve Dickson <steved@redhat.com>