Changes

s1ap_proxy: correct handling of UE CONTEXT RELEASE REQUEST

By sending a UE CONTEXT RELEASE REQUEST, the eNB is requesting the
MME to terminate the UE context.  This procedure itself does not
terminate the UE context nor the associated E-RABs.  Therefore, the
S1GW should not terminate E-RAB FSMs upon receiving this PDU.

Keep the function clause in s1ap_proxy, so that the respective
?S1GW_CTR_S1AP_PROXY_IN_PKT_RELEASE_CTX_REQ is properly updated.
Correct the unit test: E-RAB is now expected to remain alive.

Change-Id: If467162e871b7989f0578be30c04d1c32c263c99
Related: osmo-ttcn3-hacks.git Ibbb6da1f2888995608b980e7479758000e94864e
Related: SYS#7738, SYS#7599