llc_queue and codel code has been taken from osmo-pcu.git
6a5b1b1f3ef83f87a9df1d4511e22f59039e11ed and have been refactored to fit
in libosmo-gprs (removed llc_pdu structs, reworked struct types being
enqueued, etc.). Support for queues based on radio_prio has also been
added.
Related: OS#5500
Change-Id: Icdaa046fb6a71367f10beee16dcf9a5b7b61022e
