[opus] opusenc for ambisonics?

[Marc Lavallée]

I compiled the latest (git master) of opus, libopusenc, opusfile and
opus-tools:

$ opusenc --version
opusenc opus-tools 0.2-8-g4976421 (using libopus 1.3.1-4-gad8fe90d)

I tried to encode a 3rd order Ambisonics wav file with the standard
Ambix (ACN-SN3D) format; opusinfo is reporting :

Streams: 16, Coupled: 0
    Channel Mapping Family: 255 Map: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13, 14, 15]

How to encode the file so that the Mapping Family is 3, as suggested
here ? : https://people.xiph.org/~jm/opus/opus-1.3/

Marc