MME does not handle PDN Connectivity Request messages

[spencersevilla]

Problem: After a specific phone attaches to our network, it sends a "PDN Connectivity Request" message with some extra APNs that are not supported. the MME currently drops this packet; as a result, the phone re-sends the request every five seconds.

Desired Behavior: MME should send a PDN Connectivity Reject message to the UE.

Logs: EPC/Wireshark logs are not public; ping Spencer for them.

Code: There is a quick draft of a fix (unverified!!!) in branch bokondini_fixes; I think it might segfault but have not been able to verify. Relevant code is at epc/src/nas/emm/sap/emm_cn.c:214