rlcmac: Initial ul_tbf data support

This is basically an import of relevant code from osmo-pcu.git
08523c2286dfe27402f8e2eb4b98da5a529c7915 which allows encoding LLC
frames into RLC/MAC uplink data blocks.

A 1-to-1 import was not possible for several reasons:
* osmo-pcu uses C++ in some places
* osmo-pcu implements encoding of DL data blocks, not UL data blocks
* Some osmo-pcu code is still not really polished and stuff is still
  mixed (for instance rlc_window(_ul).c/h were split into their own
  files here).
Hence this was not a "copy all files and leave as they are" import, but
rather looking at the encode path starting on osmo-pcu.git scheduler and
see which code had to be pulled in to encode the RLC/MAC blocks.

Due to the slightly different requerirements for UL and DL blocks, it is
well possible that further work in needed in order to have the code
produce correct blocks. This is only a first step to pull in all code so
that stuff can be fixed in smallish incremental steps.

Related: OS#5500
Change-Id: I0a01d79d16bbfc63aa88e6bb0f432f3772645730
---
M include/osmocom/gprs/rlcmac/Makefile.am
A include/osmocom/gprs/rlcmac/coding_scheme.h
A include/osmocom/gprs/rlcmac/rlc.h
A include/osmocom/gprs/rlcmac/rlc_window.h
A include/osmocom/gprs/rlcmac/rlc_window_ul.h
M include/osmocom/gprs/rlcmac/rlcmac_enc.h
M include/osmocom/gprs/rlcmac/rlcmac_private.h
M include/osmocom/gprs/rlcmac/tbf_ul.h
M include/osmocom/gprs/rlcmac/tbf_ul_fsm.h
M src/rlcmac/Makefile.am
A src/rlcmac/coding_scheme.c
A src/rlcmac/rlc.c
A src/rlcmac/rlc_window.c
A src/rlcmac/rlc_window_ul.c
M src/rlcmac/rlcmac.c
M src/rlcmac/rlcmac_enc.c
M src/rlcmac/tbf_ul.c
M src/rlcmac/tbf_ul_fsm.c
18 files changed, 2,525 insertions(+), 9 deletions(-)