MME not looking up enb_ue_id correctly?

[spencersevilla]

We are seeing multiple instances/variants of the following issue, which appears to be related to MME not storing enb_ue_ids correctly.

eNB -> MME: InitialUEMessgae, Attach Request, enb_ue_id X
eNB <- MME: Auth Request, enb_ue_id X, mme_ue_id Y
eNB -> MME: Auth Response, enb_ue_id X, mme_ue_id Y

when the MME receives the Auth Response, the enb_ue_id lookup on X fails and we get an error:
ERROR: s1ap_handle_uplink_nas_transport: Expectation 'enb_ue' failed. (s1ap-handler.c:353).

This is strange and unexpected, in no small part because we just processed the AttachRequest for that same enb_ue_id.

pcap: 6dec_0.pcap packets 77-79.

This might be related to #13.