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