lnwire: converge discovery part of messages with specification

Change the name of fields of messages which are belong to the discovery
subsystem in a such way so they were the same with the names that are
defined in the specification.

lnwire/announcement_signatures.go

@@ -23,7 +23,7 @@ type AnnounceSignatures struct {
 	// as the block height, the next 3 bytes indicating the transaction
 	// index within the block, and the least significant two bytes
 	// indicating the output index which pays to the channel.
-	ShortChannelID ChannelID
+	ShortChannelID ShortChannelID
 
 	// NodeSignature is the signature which contains the signed announce
 	// channel message, by this signature we proof that we posses of the