[PATCH bpf-next] net: core: Fix build with CONFIG_IPV6=m

[Joe Stringer]

Stephen Rothwell reports the following link failure with IPv6 as module:

  x86_64-linux-gnu-ld: net/core/filter.o: in function `sk_lookup':
  (.text+0x19219): undefined reference to `__udp6_lib_lookup'

Fix the build by only enabling the IPv6 socket lookup if IPv6 support is
compiled into the kernel.

Signed-off-by: Joe Stringer <j...@wand.net.nz>
---
 net/core/filter.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/net/core/filter.c b/net/core/filter.c
index 591c698bc517..30c6b2d3ef16 100644
--- a/net/core/filter.c
+++ b/net/core/filter.c
@@ -4838,7 +4838,7 @@ struct sock *sk_lookup(struct net *net, struct 
bpf_sock_tuple *tuple,
                        sk = __udp4_lib_lookup(net, src4, tuple->ipv4.sport,
                                               dst4, tuple->ipv4.dport,
                                               dif, sdif, &udp_table, skb);
-#if IS_ENABLED(CONFIG_IPV6)
+#if IS_REACHABLE(CONFIG_IPV6)
        } else {
                struct in6_addr *src6 = (struct in6_addr *)&tuple->ipv6.saddr;
                struct in6_addr *dst6 = (struct in6_addr *)&tuple->ipv6.daddr;
-- 
2.17.1