MT#55283 fix not processing DTMF events while media is being blocked and DTMF-security=silence
when DTMF-security is set to an option that results in a transcode,
the packets go into handler_func_transcode. This returns immediately
when handler_silence_block returns false due to block-media, resulting
in the events not being processed for sending on log-DTMF etc.
This change only uses the transcode function for transcoded DTMF if
we're not blocking media (and logically, blocking media should mean
_all_ media). It instead goes into __handler_func_supplemental as normal
so packet_dtmf can process the packet, but drop it if its in one of
these modes and media is blocked
Change-Id: I19901877f6018f3916b22ff60799e8c74d02e065