rxrpc: Make IPv6 support conditional on CONFIG_IPV6

Add CONFIG_AF_RXRPC_IPV6 and make the IPv6 support code conditional on it.
This is then made conditional on CONFIG_IPV6.

Without this, the following can be seen:

   net/built-in.o: In function `rxrpc_init_peer':
>> peer_object.c:(.text+0x18c3c8): undefined reference to `ip6_route_output_flags'

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rxrpc/peer_event.c b/net/rxrpc/peer_event.c
index 7421758..9e0725f 100644
--- a/net/rxrpc/peer_event.c
+++ b/net/rxrpc/peer_event.c
@@ -66,6 +66,7 @@
 		}
 		break;
 
+#ifdef CONFIG_AF_RXRPC_IPV6
 	case AF_INET6:
 		srx.transport.sin6.sin6_port = serr->port;
 		srx.transport_len = sizeof(struct sockaddr_in6);
@@ -78,7 +79,7 @@
 			break;
 		case SO_EE_ORIGIN_ICMP:
 			_net("Rx ICMP on v6 sock");
-			memcpy(&srx.transport.sin6.sin6_addr.s6_addr + 12,
+			memcpy(srx.transport.sin6.sin6_addr.s6_addr + 12,
 			       skb_network_header(skb) + serr->addr_offset,
 			       sizeof(struct in_addr));
 			break;
@@ -89,6 +90,7 @@
 			break;
 		}
 		break;
+#endif
 
 	default:
 		BUG();