Encrypted packets sent from MQTT won't decrypt about firmware HOT 2 CLOSED

   * A particular node might know only a subset of channels in use on the mesh.
   * Therefore channel_index is inherently a local concept and meaningless to send between nodes.
   * Very briefly, while sending and receiving deep inside the device Router code, this field instead
   * contains the 'channel hash' instead of the index.
   * This 'trick' is only used while the payload_variant is an 'encrypted'.
   */
  uint32 channel = 3;