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/include/net/inet_common.h b/include/net/inet_common.h
index fe7994c..b2828a0 100644
--- a/include/net/inet_common.h
+++ b/include/net/inet_common.h
@@ -37,6 +37,8 @@
 int inet_ctl_sock_create(struct sock **sk, unsigned short family,
 			 unsigned short type, unsigned char protocol,
 			 struct net *net);
+int inet_recv_error(struct sock *sk, struct msghdr *msg, int len,
+		    int *addr_len);
 
 static inline void inet_ctl_sock_destroy(struct sock *sk)
 {