gnrc_lwmac: port to gnrc_netif2.

Makefile.dep

sys/auto_init/netif/auto_init_at86rf2xx.c

sys/include/net/gnrc/lwmac/hdr.h

sys/include/net/gnrc/lwmac/lwmac.h

sys/include/net/gnrc/lwmac/timeout.h

sys/include/net/gnrc/lwmac/types.h

sys/include/net/gnrc/mac/internal.h

sys/include/net/gnrc/netif2/mac.h

sys/net/gnrc/link_layer/lwmac/include/lwmac_internal.h

sys/net/gnrc/link_layer/lwmac/include/rx_state_machine.h

sys/net/gnrc/link_layer/lwmac/include/tx_state_machine.h

sys/net/gnrc/link_layer/lwmac/lwmac.c

sys/net/gnrc/link_layer/lwmac/lwmac_internal.c

sys/net/gnrc/link_layer/lwmac/rx_state_machine.c

sys/net/gnrc/link_layer/lwmac/timeout.c

sys/net/gnrc/link_layer/lwmac/tx_state_machine.c

sys/net/gnrc/netif2/gnrc_netif2_ieee802154.c