Tobias Engel ea730327d1 ussd: Reject and release unhandled SS requests/interrogation
In case the unpack of a USSD request is failing the channel would
remain open and the phone would not receive a response. Simply
reject the interrogation.

Example interrogation:
0000   1b 7b 1c 0d a1 0b 02 01 01 02 01 0e 30 03 04 01
0010   11 7f 01 00
2013-12-28 17:52:23 +01:00
2011-02-05 20:26:25 +01:00

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Osmocom Media Gateway (RTP proxy and RTP/E1 gateway)
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