rlcmac: Initial implementation of UL TBF assignment and scheduler

This patch is another towards a working RLC/MAC implementation. It adds:
* An initial data model with MS (gprs_rlcmac_entity) and ul_tbf.
* A UL_TBF state FSM from initial to FLOW status
* A UL_TBF assignemnt FSM, covering both 1phase and 2phase assignments.
* Triggering of UL_TBF allocation and assignment FSM when new LLC data
  is pushed from upper layers.
* A scheduler generating some ctrl messages (PktResReq and UlDummyCtrlBlk)
  when indicated by the network.

This patch is pushed as a WIP state since it already contains a
considerable amount of code and lots of new files, which can be
used/extended at a later point, making parallel contribution easier.

Related: OS#5500
Change-Id: I420c57a9d0b63f9c2805a7c2ae8ce85532a48eef
---
M include/osmocom/gprs/rlcmac/Makefile.am
M include/osmocom/gprs/rlcmac/rlcmac.h
A include/osmocom/gprs/rlcmac/rlcmac_enc.h
M include/osmocom/gprs/rlcmac/rlcmac_private.h
A include/osmocom/gprs/rlcmac/sched.h
A include/osmocom/gprs/rlcmac/tbf.h
A include/osmocom/gprs/rlcmac/tbf_ul.h
A include/osmocom/gprs/rlcmac/tbf_ul_ass_fsm.h
A include/osmocom/gprs/rlcmac/tbf_ul_fsm.h
A include/osmocom/gprs/rlcmac/types_private.h
M src/rlcmac/Makefile.am
M src/rlcmac/gre.c
M src/rlcmac/misc.c
M src/rlcmac/rlcmac.c
A src/rlcmac/rlcmac_enc.c
A src/rlcmac/sched.c
A src/rlcmac/tbf.c
A src/rlcmac/tbf_ul.c
A src/rlcmac/tbf_ul_ass_fsm.c
A src/rlcmac/tbf_ul_fsm.c
20 files changed, 1,272 insertions(+), 2 deletions(-)