Peers don't keep firewall ports open

[samvrlewis]

meshboi currently has some logic to ensure that the peer's firewall is open for inbound connection from other meshboi peers:

meshboi/peer_connector.go

Line 137 in c5f221b

_, err = conn.Write([]byte("hello"))

However, there currently is no mechanism to ensure that the firewall is kept open for the duration of the connection between the peers. This leads to firewall/s timing out the opened port and the connection between two peers dropping, if there is no traffic between the peers (for ufw this seems to happen after ~10mins or so).

Similar to the heartbeat that is sent to the rolodex, to ensure the NAT mapping stays open

meshboi/rolodex_client.go

Line 82 in c5f221b

_, err = c.conn.Write(b)

meshboi should also send a periodic heartbeat to all peers to ensure that its firewall ports remain open.