Begins a new net message. If another net message is already started and hasn't been sent yet, it will be discarded.
Each net message has a length limit of 64KB!
The message name must be pooled with util.AddNetworkString beforehand!
1 string messageName
The name of the message to send
2 boolean unreliable = false
If set to true, the message is not guaranteed to reach its destination
True if the message has been started.