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: ca6fb0651883 ("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>
diff --git a/include/net/request_sock.h b/include/net/request_sock.h
index dd423d8..f836694 100644
--- a/include/net/request_sock.h
+++ b/include/net/request_sock.h
@@ -92,6 +92,7 @@
 		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()