bpf: add get_netns_cookie helper to cgroup_skb programs

This is needed in the context of Cilium and Tetragon to retrieve netns
cookie from hostns when traffic leaves Pod, so that we can correlate
skb->sk's netns cookie.

Signed-off-by: Mahe Tardy <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Alexei Starovoitov <[email protected]>

Author: mtardy

net/core/filter.c

@@ -8075,6 +8075,8 @@ sk_filter_func_proto(enum bpf_func_id func_id, const struct bpf_prog *prog)
 		return &bpf_skb_load_bytes_relative_proto;
 	case BPF_FUNC_get_socket_cookie:
 		return &bpf_get_socket_cookie_proto;
+	case BPF_FUNC_get_netns_cookie:
+		return &bpf_get_netns_cookie_proto;
 	case BPF_FUNC_get_socket_uid:
 		return &bpf_get_socket_uid_proto;
 	case BPF_FUNC_perf_event_output: