rxrpc: Fix error reception on AF_INET6 sockets

AF_RXRPC tries to turn on IP_RECVERR and IP_MTU_DISCOVER on the UDP socket
it just opened for communications with the outside world, regardless of the
type of socket.  Unfortunately, this doesn't work with an AF_INET6 socket.

Fix this by turning on IPV6_RECVERR and IPV6_MTU_DISCOVER instead if the
socket is of the AF_INET6 family.

Without this, kAFS server and address rotation doesn't work correctly
because the algorithm doesn't detect received network errors.

Fixes: 75b54cb5 ("rxrpc: Add IPv6 support")
Signed-off-by: David Howells <dhowells@redhat.com>

net/rxrpc/local_object.c

@@ -134,6 +134,8 @@ static int rxrpc_open_socket(struct rxrpc_local *local, struct net *net)
 		}
 	}
 
+	switch (local->srx.transport.family) {
+	case AF_INET:
 		/* we want to receive ICMP errors */
 		opt = 1;
 		ret = kernel_setsockopt(local->socket, SOL_IP, IP_RECVERR,
@@ -151,6 +153,31 @@ static int rxrpc_open_socket(struct rxrpc_local *local, struct net *net)
 			_debug("setsockopt failed");
 			goto error;
 		}
+		break;
+
+	case AF_INET6:
+		/* we want to receive ICMP errors */
+		opt = 1;
+		ret = kernel_setsockopt(local->socket, SOL_IPV6, IPV6_RECVERR,
+					(char *) &opt, sizeof(opt));
+		if (ret < 0) {
+			_debug("setsockopt failed");
+			goto error;
+		}
+
+		/* we want to set the don't fragment bit */
+		opt = IPV6_PMTUDISC_DO;
+		ret = kernel_setsockopt(local->socket, SOL_IPV6, IPV6_MTU_DISCOVER,
+					(char *) &opt, sizeof(opt));
+		if (ret < 0) {
+			_debug("setsockopt failed");
+			goto error;
+		}
+		break;
+
+	default:
+		BUG();
+	}
 
 	/* set the socket up */
 	sock = local->socket->sk;