mgcp_test: add returncode check

The returncode of get_conn_id_from_response() is unchecked, which
is intentional since some of the test messages will intentionally cause
this function to fail (the response does not inclde a connection
identifier). This means it makes no sense to assert this function
to a fixed value.

In order to spot regressions better print a log message depending
on the return code.

Change-Id: I9bce9ca39b7751b557374b7ab57c6c9005bcdb7d
Fixes: Coverity CID#180534
2 files changed