This helper function allows BPF programs to try to generate SYN cookies, given a reference to a listener socket. The function works from XDP and with an skb context since bpf_skc_lookup_tcp can lookup a socket in both cases. Change-Id: Iac961811f33901dc0a63365669a79dcf2762fecf Signed-off-by: Petar Penkov <ppenkov@google.com> Suggested-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Lorenz Bauer <lmb@cloudflare.com> Signed-off-by: Alexei Starovoitov <ast@kernel.org> Signed-off-by: Naveen <133593113+elohim-etz@users.noreply.github.com>