tcp: push full zerocopy packets

Skbs that reach MAX_SKB_FRAGS cannot be extended further. Do the
same for zerocopy frags as non-zerocopy frags and set the PSH bit.
This improves GRO assembly.
Suggested-by: NEric Dumazet <edumazet@google.com>
Signed-off-by: NWillem de Bruijn <willemb@google.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -1371,8 +1371,10 @@ int tcp_sendmsg_locked(struct sock *sk, struct msghdr *msg, size_t size)
 			pfrag->offset += copy;
 		} else {
 			err = skb_zerocopy_iter_stream(sk, skb, msg, copy, uarg);
-			if (err == -EMSGSIZE || err == -EEXIST)
+			if (err == -EMSGSIZE || err == -EEXIST) {
+				tcp_mark_push(tp, skb);
 				goto new_segment;
+			}
 			if (err < 0)
 				goto do_error;
 			copy = err;