adb: skip IPv6 test if IPv6 isn't available.

        ipv4.listen(1)

        ipv6 = socket.socket(socket.AF_INET6, socket.SOCK_STREAM)

        try:

            ipv6.bind(('::1', ipv4.getsockname()[1] + 1))

            ipv6.listen(1)

        except socket.error:

            print("IPv6 not available, skipping")

            return

        for s in (ipv4, ipv6):

            port = s.getsockname()[1]