ipv6: export ip6_datagram_recv_ctl

ip6_datagram_recv_ctl and ip6_datagram_send_ctl are used for handling IPv6
ancillary data.  Since ip6_datagram_send_ctl is already publicly exported for
use in modules, ip6_datagram_recv_ctl should also be available to support
ancillary data in the receive path.
Signed-off-by: Tom Parkin <tparkin@katalix.com>
Signed-off-by: James Chapman <jchapman@katalix.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv6/datagram.c

@@ -598,6 +598,7 @@ int ip6_datagram_recv_ctl(struct sock *sk, struct msghdr *msg,
 	}
 	return 0;
 }
+EXPORT_SYMBOL_GPL(ip6_datagram_recv_ctl);
 
 int ip6_datagram_send_ctl(struct net *net, struct sock *sk,
 			  struct msghdr *msg, struct flowi6 *fl6,