ipv6/addrconf: call addrconf_ifdown with consistent values

Second parameter of addrconf_ifdown "how" is used as a boolean
internally. It does not make sense to call it with something different
of 0 or 1.

This value is set to 2 in all git history.
Signed-off-by: NFlorent Fourcot <florent.fourcot@wifirst.fr>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv6/addrconf.c

@@ -7189,7 +7189,7 @@ void addrconf_cleanup(void)
 			continue;
 		addrconf_ifdown(dev, 1);
 	}
-	addrconf_ifdown(init_net.loopback_dev, 2);
+	addrconf_ifdown(init_net.loopback_dev, 1);
 
 	/*
 	 *	Check hash table.