Add subchannels in DataChannels (dataProducer.send() method)

[ibc]

Mechanism to specify which DataConsumers should receive a message sent via dataProducer.send().

const dataConsumer = await transport.consumeData({
  [...],
  subchannels: [ 0, 2, 5 ]
});

const subchannels = dataConsumer.subchannels;
// => [ 0, 2, 5 ] (cloned array)

await dataConsumer.setSubchannels([ 1, 2, 5 ]);
// => Set(4) { 0, 2, 5, 4 }

const subchannels = dataConsumer.subchannels;
// => [ 1, 2, 5 ] (cloned array)

await dataConsumer.setSubchannels([]);
// => [] (cloned array)

// Send a message to all DataConsumers regardless their subchannels.
dataPoducer.send(
  message,
  /* ppid */
  undefined,
  /* subchannels */
  undefined,
  /* requiredSubchannel */
  undefined
);

// Send a message only to DataConsumers in subchannels 1 or 2.
dataPoducer.send(
  message,
  /* ppid */
  undefined,
  /* subchannels */
  [ 1, 2 ],
  /* requiredSubchannel */
  undefined
);

// Send a message only to DataConsumers in subchannels 1 or 2 but just 
// if also in subchannel 0.
dataPoducer.send(
  message,
  /* ppid */
  undefined,
  /* subchannels */
  [ 1, 2 ],
  /* requiredSubchannel */
  0
);

[jmillan]

This is done long time ago.