drivers/nrf24l01+ : added netdev implementation for nrf24l01+ transceiver

This PR is based on #1704. It contains a connection between the lowlevel part for the nrf24l01+ transceiver-driver and the netdev interface. I assume there will be several deficits, especially because this device fulfills no standard. So let's discuss this!
If `NETDEV_OPT_ADDRESS_TX_PREFIX`/`NETDEV_OPT_ADDRESS_TX_PREFIX` actually only would set/get the prefix this check wouldn't be necessary