net-timestamp: make tcp_recvmsg call ipv6_recv_error for AF_INET6 socks

TCP timestamping introduced MSG_ERRQUEUE handling for TCP sockets.
If the socket is of family AF_INET6, call ipv6_recv_error instead
of ip_recv_error.

This change is more complex than a single branch due to the loadable
ipv6 module. It reuses a pre-existing indirect function call from
ping. The ping code is safe to call, because it is part of the core
ipv6 module and always present when AF_INET6 sockets are active.

Fixes: 4ed2d765 (net-timestamp: TCP timestamping)
Signed-off-by: Willem de Bruijn <willemb@google.com>

----

It may also be worthwhile to add WARN_ON_ONCE(sk->family == AF_INET6)
to ip_recv_error.
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/ipv4/ping.c b/net/ipv4/ping.c
index 85a02a7..5d740cc 100644
--- a/net/ipv4/ping.c
+++ b/net/ipv4/ping.c
@@ -855,16 +855,8 @@
 	if (flags & MSG_OOB)
 		goto out;
 
-	if (flags & MSG_ERRQUEUE) {
-		if (family == AF_INET) {
-			return ip_recv_error(sk, msg, len, addr_len);
-#if IS_ENABLED(CONFIG_IPV6)
-		} else if (family == AF_INET6) {
-			return pingv6_ops.ipv6_recv_error(sk, msg, len,
-							  addr_len);
-#endif
-		}
-	}
+	if (flags & MSG_ERRQUEUE)
+		return inet_recv_error(sk, msg, len, addr_len);
 
 	skb = skb_recv_datagram(sk, flags, noblock, &err);
 	if (!skb)