ieee802154: move wpan-class.c to core.c

Like the wireless core.c file this file contains function for phy
allocation and freeing. Move this file to core.c to get similar
behaviour.
Signed-off-by: NAlexander Aring <alex.aring@gmail.com>
Signed-off-by: NMarcel Holtmann <marcel@holtmann.org>

net/ieee802154/Makefile

@@ -2,7 +2,7 @@ obj-$(CONFIG_IEEE802154) += ieee802154.o af_802154.o
 obj-$(CONFIG_IEEE802154_6LOWPAN) += ieee802154_6lowpan.o
 
 ieee802154_6lowpan-y := 6lowpan_rtnl.o reassembly.o
-ieee802154-y := netlink.o nl-mac.o nl-phy.o nl_policy.o wpan-class.o \
+ieee802154-y := netlink.o nl-mac.o nl-phy.o nl_policy.o core.o \
                 header_ops.o
 af_802154-y := af_ieee802154.o raw.o dgram.o