a simple serial sniffer for jennic modules. Returns the MAC_RxFrameData_s struct
from jennics Ieee802.15.4 mac layer, which contains a cropped mac packet. The
payload of the MAC_RxFrameData_s does not only contain the raw data of a packet,
but also its raw header, so a full-sized packet won't fit into MAC_RxFrameData_s
and the last few bytes of the payload will be missing.

Configuration is done by sending the channel number and a newline over the
serial port. An example pc programm is contained in sniff.py.

Special note for ftdi-based designs with custom usb ids, load the ftdi_sio
serial driver with:
 sudo modprobe ftdi_sio vendor=0x0403 product=0xcc40