tcp: no longer set skb->reserved_tailroom

TCP/MPTCP sendmsg() no longer puts payload in skb->head,
we can remove not needed code.
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/tcp.c

@@ -876,11 +876,6 @@ struct sk_buff *tcp_stream_alloc_skb(struct sock *sk, int size, gfp_t gfp,
 		}
 		if (likely(mem_scheduled)) {
 			skb_reserve(skb, MAX_TCP_HEADER);
-			/*
-			 * Make sure that we have exactly size bytes
-			 * available to the caller, no more, no less.
-			 */
-			skb->reserved_tailroom = skb->end - skb->tail - size;
 			INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
 			return skb;
 		}

net/mptcp/protocol.c

@@ -1174,7 +1174,6 @@ static struct sk_buff *__mptcp_do_alloc_tx_skb(struct sock *sk, gfp_t gfp)
 	if (likely(skb)) {
 		if (likely(__mptcp_add_ext(skb, gfp))) {
 			skb_reserve(skb, MAX_TCP_HEADER);
-			skb->reserved_tailroom = skb->end - skb->tail;
 			INIT_LIST_HEAD(&skb->tcp_tsorted_anchor);
 			return skb;
 		}