tcp: get_cookie_sock() consolidation

IPv4 and IPv6 share same implementation of get_cookie_sock(),
and there is no point inlining it.

We add tcp_ prefix to the common helper name and export it.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 2bb2bad..978cebe 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -469,6 +469,9 @@
 void inet_sk_rx_dst_set(struct sock *sk, const struct sk_buff *skb);
 
 /* From syncookies.c */
+struct sock *tcp_get_cookie_sock(struct sock *sk, struct sk_buff *skb,
+				 struct request_sock *req,
+				 struct dst_entry *dst);
 int __cookie_v4_check(const struct iphdr *iph, const struct tcphdr *th,
 		      u32 cookie);
 struct sock *cookie_v4_check(struct sock *sk, struct sk_buff *skb);