Order of media formats not preserved

[singpolyma]

When I call:

description.addOpucCodec(107);
description.addPCMUCodec(0);

I expect my m-line to contain formats in the order 107 0 so that I express that I prefer to use opus rather than PCMU when both are available. But

libdatachannel/src/description.cpp

Line 908 in fbd8f23

for (auto it = mRtpMaps.begin(); it != mRtpMaps.end(); ++it)

which generates this list pulls from a std::map which orders by key, and the payloadType is the key, so it ends up putting 0 first and PCMU wins.

Using 0 because it is the standard payloadType for PCMU https://en.wikipedia.org/wiki/RTP_payload_formats

[paullouisageneau]

Indeed currently order is not preserved. This was already mentioned by @wusspuss in #1142 with a proposed fix in #1144, however it's not finished and would break things as it is.

[paullouisageneau]

Fixed by #1168