Only listen for monitor connections on localhost by default

This is to prevent accidental exposure of the monitor port to the public
internet if a server admin enables the monitor port without it being
properly firewalled. There is now a config option that lets you override
the address to bind to, so that it can still be made available to other
machines over private networks such as Wireguard.

config.ini

@@ -102,5 +102,8 @@ eventmode=0
 enabled=false
 # the port to listen for connections on
 port=8003
+# The local IP to listen on.
+# Do not change this unless you know what you're doing.
+listenip=127.0.0.1
 # how often the listeners should be updated (in milliseconds)
 interval=5000