ussd: Decode interrogateSS that doesn't have test

Keith of Rhizomatica has an issue of a unrejected interrogateSS.
Start with just decoding the message and printing the empty test
and the code.

What is kind of missing is the classification between invoke,
returnResult and returnResultLast that we need to add in the
long run.

Change-Id: Iadfa156707a96f2a34f3948c7cc9a74435f17114
diff --git a/tests/ussd/ussd_test.ok b/tests/ussd/ussd_test.ok
index 54d59ee..69ea53c 100644
--- a/tests/ussd/ussd_test.ok
+++ b/tests/ussd/ussd_test.ok
@@ -1,4 +1,5 @@
 Tested if it still works. Text was: **321#
+interrogateSS CFU text..'' code 33
 Testing parsing a USSD request and truncated versions
 Result for 1 is 28
 Result for 1 is 27