ipv6: export fib6_lookup for nft_fib_ipv6

Upcoming patch will call fib6_lookup from nft_fib_ipv6.  The EXPORT_SYMBOL is
added twice because there are two implementations of the function, one
is a small stub for MULTIPLE_TABLES=n, only one is compiled into the
kernel depending on .config settings.

Alternative to EXPORT_SYMBOL is to use an indirect call via the
ipv6_stub->fib6_lookup() indirection, but thats more expensive than the
direct call.

Also, nft_fib_ipv6 cannot be builtin if ipv6 is a module.

Signed-off-by: Florian Westphal <fw@strlen.de>

net/ipv6/fib6_rules.c

@@ -92,6 +92,9 @@ int fib6_lookup(struct net *net, int oif, struct flowi6 *fl6,
 
 	return err;
 }
+#if IS_MODULE(CONFIG_NFT_FIB_IPV6)
+EXPORT_SYMBOL_GPL(fib6_lookup);
+#endif
 
 struct dst_entry *fib6_rule_lookup(struct net *net, struct flowi6 *fl6,
 				   const struct sk_buff *skb,

net/ipv6/ip6_fib.c

@@ -342,6 +342,9 @@ int fib6_lookup(struct net *net, int oif, struct flowi6 *fl6,
 	return fib6_table_lookup(net, net->ipv6.fib6_main_tbl, oif, fl6,
 				 res, flags);
 }
+#if IS_MODULE(CONFIG_NFT_FIB_IPV6)
+EXPORT_SYMBOL_GPL(fib6_lookup);
+#endif
 
 static void __net_init fib6_tables_init(struct net *net)
 {