[IPV6]: Remove unused method declaration in include/net/addrconf.h.

This patches removes unused declaration of addrconf_forwarding_on() method
in include/net/addrconf.h.
Signed-off-by: Rami Rosen <ramirose@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/addrconf.h

@@ -185,7 +185,6 @@ static inline void in6_ifa_put(struct inet6_ifaddr *ifp)
 #define in6_ifa_hold(ifp)	atomic_inc(&(ifp)->refcnt)
 
 
-extern void			addrconf_forwarding_on(void);
 /*
  *	Hash function taken from net_alias.c
  */