This patch adds checking the "CRC_OK" bit at the end of packets coming
from the CC2520 radio. It also adds support for putting the radio in
promiscuous mode (in which packets are not dropped if the CRC fails).
In promiscuous mode the AUTOCRC flag is cleared so that the driver can
pass the received CRC to the monitors.

The radio now defaults to frame filtering (checking that the destination
and PANID in the incoming packet matches the local node). This matches
the other 15.4 radios and is what a user would expect to be the default.

Other changes:

1. Adds LQI calculation
2. Makes #defines for relevant bit fields in CC2520 registers

Signed-off-by: Brad Campbell <bradjc5@gmail.com>
Acked-by: Varka Bhadram <varkabhadram@gmail.com>
Signed-off-by: Marcel Holtmann <marcel@holtmann.org>