[proaudio] bug: jack-audio-connection-kit need opus custom modes

[Xavier Miller <xavier.miller@xxxxxxxxx>]

Hello,

Since media-libs/opus-1.0.2, the custom modes are not automatically  
build, there is now a custom-mode USE added.

I discovered it when I tried to rebuild jack.

For now, I added a package.use entry, but it should be nice to add it  
to the jack ebuild.

Kind regards,
Xavier Miller.