lnwire/channel_update: add String method for ChanUpdate[Chan|Msg]Flags

In this commit, we fix the problem where it's annoying to parse a
bitfield printed out in decimal by writing a String method for the
ChanUpdate[Chan|Msg]Flags bitfield.

Co-authored-by: Johan T. Halseth <johanth@gmail.com>

lnwire/channel_update.go

@@ -2,6 +2,7 @@ package lnwire
 
 import (
 	"bytes"
+	"fmt"
 	"io"
 	"io/ioutil"
 
@@ -12,6 +13,11 @@ import (
 // present in the ChannelUpdate.
 type ChanUpdateMsgFlags uint8
 
+// String returns the bitfield flags as a string.
+func (c ChanUpdateMsgFlags) String() string {
+	return fmt.Sprintf("%08b", c)
+}
+
 // ChanUpdateChanFlags is a bitfield that signals various options concerning a
 // particular channel edge. Each bit is to be examined in order to determine
 // how the ChannelUpdate message is to be interpreted.
@@ -29,6 +35,11 @@ const (
 	ChanUpdateDisabled
 )
 
+// String returns the bitfield flags as a string.
+func (c ChanUpdateChanFlags) String() string {
+	return fmt.Sprintf("%08b", c)
+}
+
 // ChannelUpdate message is used after channel has been initially announced.
 // Each side independently announces its fees and minimum expiry for HTLCs and
 // other parameters. Also this message is used to redeclare initially set