UserKt

Broadcast when a newly powered mesh node wants to find a node num it can use
Sent from the phone over bluetooth to set the user id for the owner of this node.
Also sent from nodes to each other when a new node signs on (so all clients can have this info)
The algorithm is as follows:
when a node starts up, it broadcasts their user and the normal flow is for all
other nodes to reply with their User as well (so the new node can build its nodedb)
If a node ever receives a User (not just the first broadcast) message where
the sender node number equals our node number, that indicates a collision has
occurred and the following steps should happen:
If the receiving node (that was already in the mesh)'s macaddr is LOWER than the
new User who just tried to sign in: it gets to keep its nodenum.
We send a broadcast message of OUR User (we use a broadcast so that the other node can
receive our message, considering we have the same id - it also serves to let
observers correct their nodedb) - this case is rare so it should be okay.
If any node receives a User where the macaddr is GTE than their local macaddr,
they have been vetoed and should pick a new random nodenum (filtering against
whatever it knows about the nodedb) and rebroadcast their User.
A few nodenums are reserved and will never be requested:
0xff - broadcast
0 through 3 - for future use