Give MessageSendInstructions any Destination, not only Blinded

In the next commit we'll use `MessageSendInstructions` for all
messages, so it needs the ability to take any `Destination`, not
only a `Destination::Blinded`.

Author: TheBlueMatt

lightning/src/onion_message/messenger.rs

@@ -367,7 +367,7 @@ impl Responder {
 	/// Use when the recipient doesn't need to send back a reply to us.
 	pub fn respond<T: OnionMessageContents>(self, response: T) -> Option<(T, MessageSendInstructions)> {
 		Some((response, MessageSendInstructions::WithoutReplyPath {
-			send_path: self.reply_path,
+			destination: Destination::BlindedPath(self.reply_path),
 		}))
 	}
 
@@ -376,7 +376,7 @@ impl Responder {
 	/// Use when the recipient needs to send back a reply to us.
 	pub fn respond_with_reply_path<T: OnionMessageContents>(self, response: T, context: MessageContext) -> Option<(T, MessageSendInstructions)> {
 		Some((response, MessageSendInstructions::WithReplyPath {
-			send_path: self.reply_path,
+			destination: Destination::BlindedPath(self.reply_path),
 			context: context,
 		}))
 	}
@@ -389,7 +389,7 @@ pub enum MessageSendInstructions {
 	/// respond.
 	WithReplyPath {
 		/// The desination where we need to send our message.
-		send_path: BlindedMessagePath,
+		destination: Destination,
 		/// The context to include in the reply path we'll give the recipient so they can respond
 		/// to us.
 		context: MessageContext,
@@ -398,7 +398,7 @@ pub enum MessageSendInstructions {
 	/// recipient from responding.
 	WithoutReplyPath {
 		/// The desination where we need to send our message.
-		send_path: BlindedMessagePath,
+		destination: Destination,
 	}
 }
 
@@ -1324,9 +1324,9 @@ where
 	pub fn handle_onion_message_response<T: OnionMessageContents>(
 		&self, response_message: T, response: MessageSendInstructions,
 	) -> Result<Option<SendSuccess>, SendError> {
-		let (response_path, context) = match response {
-			MessageSendInstructions::WithReplyPath { send_path, context } => (send_path, Some(context)),
-			MessageSendInstructions::WithoutReplyPath { send_path } => (send_path, None),
+		let (destination, context) = match response {
+			MessageSendInstructions::WithReplyPath { destination, context } => (destination, Some(context)),
+			MessageSendInstructions::WithoutReplyPath { destination } => (destination, None),
 		};
 
 		let message_type = response_message.msg_type();
@@ -1345,7 +1345,7 @@ where
 		} else { None };
 
 		self.find_path_and_enqueue_onion_message(
-			response_message, Destination::BlindedPath(response_path), reply_path,
+			response_message, destination, reply_path,
 			format_args!(
 				"when responding with {} to an onion message",
 				message_type,