Changes

erab_fsm: handle E-RAB SETUP Rsp during release

It is quite common in production for a UE context to be established
and then released before the eNB has acknowledged its creation.  In
the current implementation, this leads to errors and causes the PDU
that triggers the late E-RAB SETUP Response event to be dropped.

Make the FSM logic more flexible by handling late erab_setup_rsp
event in state erab_wait_release_rsp, i.e. during the release.
This way we avoid dropping PDUs and printing errors.

Change-Id: I17414aad42507b64e933c80a220bfbe3798a4ad0
Related: SYS#7738, SYS#7599