SS/USSD: release IUSE sessions immediately after response

At the moment, all available IUSE handlers do assume a single
request-response operation, e.g. MS requests its MSISDN - IUSE
responds. No further nor intermediate communications is required.

Let's immediately terminate such SS sessions in order to avoid
waiting for the session inactivity watchdog (i.e. timeout).

Change-Id: Iaefe37512da79e10fbe92378236bfff0eae0f8b9
1 file changed