decode: Add bitvec based GPRS DL ACK/NACK decoder

Currently the RBB is used and passed directly to the window handling
methods. For EGPRS a more abstract bitvec is derived from the messages
and will passed around instead.

Add a similar function for GPRS so that the same window handling can
be used for GPRS and EGPRS.

Sponsored-by: On-Waves ehf
2 files changed