lnwire: re-add .String() to the lnwire.Message interface

lnwire/message.go

@@ -69,6 +69,7 @@ type Message interface {
 	Command() uint32
 	MaxPayloadLength(uint32) uint32
 	Validate() error
+	String() string
 }
 
 // makeEmptyMessage creates a new empty message of the proper concrete type