support RAB Assignment in cn_ranap_rx_*_msg_co()

Allow decoding all Assignment Request/Response messages.

A RAB Assignment request is
- connection oriented
- 'initiatingMessage'
- procedureCode == RAB_Assignment

A RAB Assignment response is
- connection oriented
- 'successfulOutcome' or 'unsuccessfulOutcome' or 'outcome'
  (3GPP TS 25.413 specifies RAB Assignment as a "Class 3 Elementary
  Procedure", but doesn't seem to specify which of these three 'outcome'
  types to use for Class 3. In the field we've seen 'successfulOutcome'
  and 'outcome'. Either one is fine.)
- procedureCode == RAB_Assignment

Add decoding the request to cn_ranap_rx_initiating_msg_co().
Add decoding the unsuccessful response to
cn_ranap_rx_unsuccessful_msg_co();

Decoding the successful response is already present in
cn_ranap_rx_successful_msg_co().

osmo-gsm-shark uses this to connect a voice call's signalling with RTP.

Change-Id: Ifec566a98cb6141d27b9e5e33d5a78f8b1530658
---
M src/ranap_common_cn.c
1 file changed, 46 insertions(+), 0 deletions(-)