bpf: Add sockmap hooks for UDP sockets

Add basic psock hooks for UDP sockets. This allows adding and
removing sockets, as well as automatic removal on unhash and close.

Signed-off-by: Lorenz Bauer <lmb@cloudflare.com>
Signed-off-by: Jakub Sitnicki <jakub@cloudflare.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>
Acked-by: John Fastabend <john.fastabend@gmail.com>
Link: https://lore.kernel.org/bpf/20200309111243.6982-8-lmb@cloudflare.com
diff --git a/include/net/udp.h b/include/net/udp.h
index e55d5f7..a8fa6c0 100644
--- a/include/net/udp.h
+++ b/include/net/udp.h
@@ -503,4 +503,9 @@ static inline struct sk_buff *udp_rcv_segment(struct sock *sk,
 	return segs;
 }
 
+#ifdef CONFIG_BPF_STREAM_PARSER
+struct sk_psock;
+struct proto *udp_bpf_get_proto(struct sock *sk, struct sk_psock *psock);
+#endif /* BPF_STREAM_PARSER */
+
 #endif	/* _UDP_H */