lnwire: Add BOLT#1 'init' message

'init' message is the first message reveals the features supported or required
by this node. Nodes wait for receipt of the other's features to simplify error
diagnosis where features are incompatible. This message will help negotioate the
the features which are supported by both sides.

lnwire/message.go

@@ -22,6 +22,8 @@ const MaxMessagePayload = 1024 * 1024 * 32 //  32MB
 
 // Commands used in lightning message headers which detail the type of message.
 const (
+	CmdInit = uint32(1)
+
 	// Commands for opening a channel funded by one party (single funder).
 	CmdSingleFundingRequest      = uint32(100)
 	CmdSingleFundingResponse     = uint32(110)
@@ -88,6 +90,8 @@ func makeEmptyMessage(command uint32) (Message, error) {
 	var msg Message
 
 	switch command {
+	case CmdInit:
+		msg = &Init{}
 	case CmdSingleFundingRequest:
 		msg = &SingleFundingRequest{}
 	case CmdSingleFundingResponse: