selftests: Add ipv6 ping tests to fcnal-test

Add IPv6 ping tests to fcnal-test.sh. Covers the permutations of directly
connected addresses, routed destinations, VRF and non-VRF, and expected
failures.

Setup includes unreachable routes and fib rules blocking traffic.

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