coindsp patch breaks faxing

[lachesis]

I was able to reproduce this simply doing a fax from one PJSIP trunk to another. My exact call topology is:

PSTN -> (pjsip trunk) -> Asterisk 21 -> (pjsip trunk) -> Cisco 2921 -> (fxs) -> Brother FAX machine

With the coindsp patch applied, I get a bunch of this in the logs:

[May 20 18:26:06] WARNING[621039][C-0000030a]: res_rtp_asterisk.c:4309 ast_rtp_dtmf_begin: Don't know how to represent '-'
[May 20 18:26:07] WARNING[621039][C-0000030a]: res_rtp_asterisk.c:4431 ast_rtp_dtmf_end_with_duration: Don't know how to represent '-'

And my faxes all fail with complaints about poor line quality. If I reverse that patch and restart Asterisk, the issues disappear. As I don't have any kind of coin phones attached to my system, I'll just keep this one reverted.

Reverting can be done by:

# go to your asterisk source directory
cd /usr/src/asterisk-*

# download the patch
wget -O /tmp/coindsp.patch https://raw.githubusercontent.com/InterLinked1/phreakscript/448f7e7d099bda3b709717ab099f080a9880a52e/patches/coindsp.patch

# revert the patch
sudo patch -p1 -R < /tmp/coindsp.patch

# rebuild and install
sudo make
sudo make install