fix kernel build in non-INET6 case

[Johannes Hofmann]

Probabely due to the recent -Werror introduction kernel no longer
builds if INET6 is not set (static function declared but never
defined), so declare it only if INET6 is set:


diff --git a/sys/net/faith/if_faith.c b/sys/net/faith/if_faith.c
index 1fe2f28..650b844 100644
--- a/sys/net/faith/if_faith.c
+++ b/sys/net/faith/if_faith.c
@@ -99,7 +99,9 @@ static int faithioctl (struct ifnet *, u_long, caddr_t, struct ucred *);
 int faithoutput (struct ifnet *, struct mbuf *, struct sockaddr *,
 	struct rtentry *);
 static void faithrtrequest (int, struct rtentry *, struct rt_addrinfo *);
+#ifdef INET6
 static int faithprefix (struct in6_addr *);
+#endif
 
 static int faithmodevent (module_t, int, void *);
 

Cheers,
Johannes