bpf: selftests: test skb->tstamp in redirect_neigh

This patch adds tests on forwarding the delivery_time for
the following cases
- tcp/udp + ip4/ip6 + bpf_redirect_neigh
- tcp/udp + ip4/ip6 + ip[6]_forward
- bpf_skb_set_delivery_time
- The old rcv timestamp expectation on tc-bpf@ingress

Signed-off-by: Martin KaFai Lau <kafai@fb.com>
Signed-off-by: David S. Miller <davem@davemloft.net>