* refactor some common methods to mac_common.cc
* add common mux_base class
* move UL PDU generation to mux class
* add logical channel registration to MAC, MUX, BSR
* add initial proc BSR
* add basic MAC NR test
* rework MAC interfaces
inspired by accepted (but not yet merged) PR to include the
(unique_)byte_buffer_t for MAC/PHY interfacing, this patch adds
a few more useful bits to that. Buffer management for UL data is now
done in MAC and only a pointer to the data is passed in the UL action.
* Move Tx softbuffer to MAC (until UL HARQ class is ready)
* Remove temparal data member in cc_worker
* Remove memcpy after packing MAC PDU
after adding the thread-safe PCAP writer functionality to the EUTRA
MAC object it became clear that we don't wont to replicate the
same for the NR object.
This patch therefore refactors the class that now supports both EUTRA and
NR rats. The old mac_nr_pcap.[h/cc] has been deleted. All test-cases
and usages now use the new object that needs to pass the RAT type in
the ctor.
this patch addresses the last open point of #2160