Send disconnection reason when closing connection with a node

[lock9]

(Originally from @decentralisedkev on #366)

Summary
When a node sends an incompatible message during the handshake or a malformed message, the node silently disconnects. This makes it hard to debug why two nodes are not communicating, or why one node has disconnected from another.

Do you have any solution you want to propose?
If a node disconnects from another node, due to the message that that node had sent, they should send a reject message, stating why the node was disconnected and a byte to signify the reason for the computer.

Where in the software does this update applies to?

• P2P (TCP)

[ixje]

What reasons should we have?

• max connection limit reached
• inactivity
• shutting down
• protocol exception (e.g. handshake payload order wrong)
• format exception (caused by deserialization failures)

The first 2 can help a client in filtering good addresses. For example; if a node force disconnects me, I would now label it as a bad node because it is doing something unexpected. With the above I could differentiate if it's a "soft" disconnect or a hard disconnect because there's something really wrong.

[shargon]

We can send the reason with the peers for example.

[ixje]

We can send the reason with the peers for example.

I don't understand, what 'peers'?
My understanding of the proposal is that this is an exchange between the local client and exactly 1 remote node.

[Tommo-L]

fixed in #1154, plz review it