This includes:
- Adding a queue (implemented with std::map) for undelivered PDUs.
This queue uses the SN used for TX as the key.
- Added discard timer that is started upon reception of the SDU. Upon
expiry of the timeout a discard callback removes undelivered PDUs
from the queue.
- Added the mechanisms to the notify_delivery to remove PDUs from the
undelivered queue when the PDU is ACK'ed.
- Added test case for both timer expiry and acknowledgment.
- Fix up the getter for buffered SDUs to return the undelivered SDUs
- Changed default PDCP discard timer, so AM has a discard timer by
default.
Pedro Alvarez