bpf: sockmap, BPF_F_INGRESS flag for BPF_SK_SKB_STREAM_VERDICT:

Add support for the BPF_F_INGRESS flag in skb redirect helper. To
do this convert skb into a scatterlist and push into ingress queue.
This is the same logic that is used in the sk_msg redirect helper
so it should feel familiar.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>

net/core/filter.c

@@ -1855,7 +1855,7 @@ BPF_CALL_4(bpf_sk_redirect_map, struct sk_buff *, skb,
 	struct tcp_skb_cb *tcb = TCP_SKB_CB(skb);
 
 	/* If user passes invalid input drop the packet. */
-	if (unlikely(flags))
+	if (unlikely(flags & ~(BPF_F_INGRESS)))
 		return SK_DROP;
 
 	tcb->bpf.key = key;