net: use sk_fullsock() in __netdev_pick_tx()

SYN_RECV & TIMEWAIT sockets are not full blown, they do not have a
sk_dst_cache pointer.

Fixes: ca6fb06 ("tcp: attach SYNACK messages to request sockets instead of listener")
Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

Author: edumazet

include/net/request_sock.h

@@ -92,6 +92,7 @@ reqsk_alloc(const struct request_sock_ops *ops, struct sock *sk_listener)
 		req->rsk_listener = sk_listener;
 		req_to_sk(req)->sk_prot = sk_listener->sk_prot;
 		sk_node_init(&req_to_sk(req)->sk_node);
+		sk_tx_queue_clear(req_to_sk(req));
 		req->saved_syn = NULL;
 		/* Following is temporary. It is coupled with debugging
 		 * helpers in reqsk_put() & reqsk_free()

net/core/dev.c

@@ -2974,6 +2974,7 @@ static u16 __netdev_pick_tx(struct net_device *dev, struct sk_buff *skb)
 			new_index = skb_tx_hash(dev, skb);
 
 		if (queue_index != new_index && sk &&
+		    sk_fullsock(sk) &&
 		    rcu_access_pointer(sk->sk_dst_cache))
 			sk_tx_queue_set(sk, new_index);