selftests: Add ipv6 udp tests to fcnal-test

Add IPv6 udp tests to fcnal-test.sh. Covers the permutations of directly
connected addresses, routed destinations, VRF and non-VRF, and expected
failures for both clients and servers. Includes permutations with
net.ipv4.udp_l3mdev_accept set to 0 and 1.

Signed-off-by: David Ahern <dsahern@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>