GTP: refactor the echo timer

Move the check of the echo timer into an own function.
The gtp echo timer must be re-check everytime the
echo-timer has been modified or deactivated via vty.

Fixes the TTCN3 SGSN_Tests.TC_attach_restart_ctr_echo

Change-Id: Ia33471a9a9cfc3887facb665c82094b99932052a
3 files changed