library/RLCMAC: Add partial support for EGPRS data block encoding/decoding

* RlcmacUlBlock and RlcmacDlBlock gain a new union field "egprs_data",
  which is chosen when msg contains an egprs data block. Hence one can
  use same structure for both gprs/egprs data and simply check
  "ischosen(block.data_egprs)" to know whether it contains egprs or gprs
  data block.
* C++ code in RLCMAC_EncDec.cc takes care of encoding and decoding of
  each data header type and exposes a generic ttcn3 struct
  "UlMacDataHeader" and "DlMacDataHeader". Decoded header type can be
  found in mac_hdr.header_type. This can be used t5ogether with CPS to
  get the MCS of the message received. Similarly, the encoder will use the
  same field to know how to encode the ttcn3 structure.
* In RLCMAC_EncDec.cc order of functions has been ordered to split
  between encoding and decoding, and inside these split between Ul and
  Dl messages.
* Only encoding of UL HeaderType3 and decoding of Dl HeaderType3 is
  implemented so far in RLCMAC_EncDec.cc. However, all code is already
  arranged and functions prepared (with FIXME fprintf) to easily add the
  missing header types once needed.
* Actually only the decoding of DL HeaderType3 has been tested to work so far.
  Encoding may still be missing to octet-align the data block after the header.
  All these wil lbe fixed once a test using them exists.

Change-Id: I2bc4f877a5e17c57ffa8cf05565dc8593b45aae8
2 files changed