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

lnwire/pong.go

@@ -1,6 +1,9 @@
 package lnwire
 
-import "io"
+import (
+	"fmt"
+	"io"
+)
 
 // Ping defines a message which is sent by peers periodically to determine if
 // the connection is still valid. Each ping message should carry a unique nonce
@@ -74,3 +77,10 @@ func (p Ping) MaxPayloadLength(uint32) uint32 {
 func (p *Ping) Validate() error {
 	return nil
 }
+
+// String returns the string representation of the target Ping.
+//
+// This is part of the lnwire.Message interface.
+func (p *Ping) String() string {
+	return fmt.Sprintf("Ping(%v)", p.Nonce)
+}