[breaking] move `uplink_enabled` & `downlink_enabled` out of `ChannelSettings`

[andrekir]

https://github.com/meshtastic/protobufs/blob/master/meshtastic/channel.proto#L75-L84

There is no need to have uplink_enabled and downlink_enabled as part of ChannelSettings and ChannelSet since they don't need to be shared with all nodes in a local mesh to be able to communicate.

[thebentern]

Seems like a good item for the 3.0 project board