dtmf generation problem on K3765 about asterisk-chan-dongle HOT 3 OPEN

return -1 from channel_digit_begin() is want asterisk core to generate DTMF 
inband 

Yes, I know that returning -1 would result in asterisk generating the dtmf. I 
was just curious to find out why the code exists to have the dongle generate 
dtmf. Is it just historic, or maybe the dongle-generated dtmf is more reliable 
due to dongle-internal volume control?
If there is no real advantage in dongle-generated dtmf, the more clean solution 
(imho) would be to just delegate it to asterisk. If there is an advantage, that 
should be documented...

Of course, this bugreport is about a bug in some code, maybe in the dongle 
firmware, maybe somewhere else, so it is still a good idea to find out if we 
can track this issue down and fix it anyway, regardless of the question who 
should generate dtmf ;-)
If it's in the dongle firmware, maybe that should be documented as well.

Did some more testing with this.

When IVR system is not responding to DTMF keys, it also doesn't work when 
generating inband DTMF (i.e. playing dtmf digits and holding receiver in front 
of speakers).
When hanging up and redialing, it worked again, so no dongle reset/reload 
necessary. Generated inband dtmf through speakers also works after redialing, 
so should have worked even if DTMF generation in the dongle was bugged.

So, maybe it's not the dtmf generation that's bugged, but maybe it's the audio 
not being sent to the remote party...
I'll switch the dongle to 2G-only mode and use a radio to find out whether or 
not it is sending anything at all when dtmf in the menu isn't working ;-)

(There is a slight chance the provider's IVR isn't detecting DTMF due to a 
problem with their system, but that's not very likely.)