nativenet: Port nativenet for netdev

To test this, run

```
export BOARD=native
SENDER=0 make -C tests/netdev/ all flash && SENDER=1 make -C tests/netdev/ all flash && make -C tests/netdev/ test
```

~~Depends on #1492:~~ (it's merged)

```
* #1680
|\
… …
| |
| * #1448
| |\
* | | #1733
| * | #1732
| | * #1731
| |/
|/
* (master)
```
* To the first point: Like I did [here](https://github.com/RIOT-OS/RIOT/blob/master/tests/netdev/main.c#L34)?
* To the second: Maybe, but that's only a matter of opinion IMHO