s1gw: TC_e_rab_setup: complete E-RAB releaseThe MME originated E-RAB RELEASE procedure includes both:* [ENB <- MME] E-RAB RELEASE COMMAND, and* [ENB -> MME] E-RAB RELEASE RESPONSE.The later was overlooked in a99224c9, so add it.Change-Id: I856248d825b6ecf0635590b7bf02593cfae893d3Fixes: a99224c9 "s1gw: TC_e_rab_setup: also test E-RAB release"