packet: fix second argument of sock_tx_timestamp()

This patch fixes an issue that a syscall (e.g. sendto syscall) cannot
work correctly. Since the sendto syscall doesn't have msg_control buffer,
the sock_tx_timestamp() in packet_snd() cannot work correctly because
the socks.tsflags is set to 0.
So, this patch sets the socks.tsflags to sk->sk_tsflags as default.

Fixes: c14ac9451c34 ("sock: enable timestamping using control messages")
Reported-by: Kazuya Mizuguchi <kazuya.mizuguchi.ks@renesas.com>
Reported-by: Keita Kobayashi <keita.kobayashi.ym@renesas.com>
Signed-off-by: Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>
Acked-by: Soheil Hassas Yeganeh <soheil@google.com>
Acked-by: Willem de Bruijn <willemb@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/packet/af_packet.c

@@ -1927,7 +1927,7 @@ retry:
 		goto out_unlock;
 	}
 
-	sockc.tsflags = 0;
+	sockc.tsflags = sk->sk_tsflags;
 	if (msg->msg_controllen) {
 		err = sock_cmsg_send(sk, msg, &sockc);
 		if (unlikely(err)) {
@@ -2678,7 +2678,7 @@ static int tpacket_snd(struct packet_sock *po, struct msghdr *msg)
 		dev = dev_get_by_index(sock_net(&po->sk), saddr->sll_ifindex);
 	}
 
-	sockc.tsflags = 0;
+	sockc.tsflags = po->sk.sk_tsflags;
 	if (msg->msg_controllen) {
 		err = sock_cmsg_send(&po->sk, msg, &sockc);
 		if (unlikely(err))
@@ -2881,7 +2881,7 @@ static int packet_snd(struct socket *sock, struct msghdr *msg, size_t len)
 	if (unlikely(!(dev->flags & IFF_UP)))
 		goto out_unlock;
 
-	sockc.tsflags = 0;
+	sockc.tsflags = sk->sk_tsflags;
 	sockc.mark = sk->sk_mark;
 	if (msg->msg_controllen) {
 		err = sock_cmsg_send(sk, msg, &sockc);