Changes

erab_fsm: fix comment inaccuracies and a typo

Two comments copy-pasted from session_establish were left saying
"ESTABLISH Req" in session_modify and session_delete handlers where
"MODIFY Req" and "DELETE Req" are correct respectively.
Also fix typo "unieue" -> "unique" in init/1.

Change-Id: If84638142988767363aa080012b44082dee39f90