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_object.c b/net/rxrpc/peer_object.c
index dfc07b4..f3e5766 100644
--- a/net/rxrpc/peer_object.c
+++ b/net/rxrpc/peer_object.c
@@ -52,11 +52,13 @@
 		size = sizeof(srx->transport.sin.sin_addr);
 		p = (u16 *)&srx->transport.sin.sin_addr;
 		break;
+#ifdef CONFIG_AF_RXRPC_IPV6
 	case AF_INET6:
 		hash_key += (u16 __force)srx->transport.sin.sin_port;
 		size = sizeof(srx->transport.sin6.sin6_addr);
 		p = (u16 *)&srx->transport.sin6.sin6_addr;
 		break;
+#endif
 	default:
 		WARN(1, "AF_RXRPC: Unsupported transport address family\n");
 		return 0;
@@ -100,12 +102,14 @@
 			memcmp(&peer->srx.transport.sin.sin_addr,
 			       &srx->transport.sin.sin_addr,
 			       sizeof(struct in_addr));
+#ifdef CONFIG_AF_RXRPC_IPV6
 	case AF_INET6:
 		return ((u16 __force)peer->srx.transport.sin6.sin6_port -
 			(u16 __force)srx->transport.sin6.sin6_port) ?:
 			memcmp(&peer->srx.transport.sin6.sin6_addr,
 			       &srx->transport.sin6.sin6_addr,
 			       sizeof(struct in6_addr));
+#endif
 	default:
 		BUG();
 	}
@@ -159,7 +163,9 @@
 	struct rtable *rt;
 	struct flowi fl;
 	struct flowi4 *fl4 = &fl.u.ip4;
+#ifdef CONFIG_AF_RXRPC_IPV6
 	struct flowi6 *fl6 = &fl.u.ip6;
+#endif
 
 	peer->if_mtu = 1500;
 
@@ -177,6 +183,7 @@
 		dst = &rt->dst;
 		break;
 
+#ifdef CONFIG_AF_RXRPC_IPV6
 	case AF_INET6:
 		fl6->flowi6_iif = LOOPBACK_IFINDEX;
 		fl6->flowi6_scope = RT_SCOPE_UNIVERSE;
@@ -191,6 +198,7 @@
 			return;
 		}
 		break;
+#endif
 
 	default:
 		BUG();
@@ -241,9 +249,11 @@
 	case AF_INET:
 		peer->hdrsize = sizeof(struct iphdr);
 		break;
+#ifdef CONFIG_AF_RXRPC_IPV6
 	case AF_INET6:
 		peer->hdrsize = sizeof(struct ipv6hdr);
 		break;
+#endif
 	default:
 		BUG();
 	}