bpf: also call skb_postpush_rcsum on xmit occasions

Follow-up to commit f8ffad69 ("bpf: add skb_postpush_rcsum and fix
dev_forward_skb occasions") to fix an issue for dev_queue_xmit() redirect
locations which need CHECKSUM_COMPLETE fixups on ingress.

For the same reasons as described in f8ffad69 already, we of course
also need this here, since dev_queue_xmit() on a veth device will let us
end up in the dev_forward_skb() helper again to cross namespaces.

Latter then calls into skb_postpull_rcsum() to pull out L2 header, so
that netif_rx_internal() sees CHECKSUM_COMPLETE as it is expected. That
is, CHECKSUM_COMPLETE on ingress covering L2 _payload_, not L2 headers.

Also here we have to address bpf_redirect() and bpf_clone_redirect().

Fixes: 3896d655 ("bpf: introduce bpf_clone_redirect() helper")
Fixes: 27b29f63

 ("bpf: add bpf_redirect() helper")
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>