ieee802154: make wpan-phy class registration to subsys_initcall

Move ieee802154 initialisation to subsys_initcall call, so that
wpan-phy class is initialised before all devices (thus saving us from
oops during bootup).
Signed-off-by: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>

net/ieee802154/wpan-class.c

@@ -205,7 +205,7 @@ err_nl:
 err:
 	return rc;
 }
-module_init(wpan_phy_class_init);
+subsys_initcall(wpan_phy_class_init);
 
 static void __exit wpan_phy_class_exit(void)
 {