net: implement tcp coalescing in tcp_queue_rcv()

Extend tcp coalescing implementing it from tcp_queue_rcv(), the main
receiver function when application is not blocked in recvmsg().

Function tcp_queue_rcv() is moved a bit to allow its call from
tcp_data_queue()

This gives good results especially if GRO could not kick, and if skb
head is a fragment.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Alexander Duyck <alexander.h.duyck@intel.com>
Cc: Neal Cardwell <ncardwell@google.com>
Cc: Tom Herbert <therbert@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/tcp.h b/include/net/tcp.h
index 5283aa4..c826ed7 100644
--- a/include/net/tcp.h
+++ b/include/net/tcp.h
@@ -439,7 +439,8 @@
 
 void tcp_connect_init(struct sock *sk);
 void tcp_finish_connect(struct sock *sk, struct sk_buff *skb);
-void tcp_queue_rcv(struct sock *sk, struct sk_buff *skb, int hdrlen);
+int __must_check tcp_queue_rcv(struct sock *sk, struct sk_buff *skb,
+			       int hdrlen, bool *fragstolen);
 
 /* From syncookies.c */
 extern __u32 syncookie_secret[2][16-4+SHA_DIGEST_WORDS];