Make ChannelManager::create_blinded_path context-type-generic

In the next commit we'll want to use `create_blinded_path` to build
a blinded path with a `DNSResolverContext` rather than an
`OffersContext`. In order to do so, it needs to take a generic
`MessageContext` rather than an `OffersContext`, which we let it
here.

Author: TheBlueMatt

lightning/src/ln/channelmanager.rs

@@ -9086,7 +9086,7 @@ where
 
 		let hmac = payment_id.hmac_for_offer_payment(nonce, expanded_key);
 		let context = OffersContext::OutboundPayment { payment_id, nonce, hmac: Some(hmac) };
-		let reply_paths = self.create_blinded_paths(context)
+		let reply_paths = self.create_blinded_paths(MessageContext::Offers(context))
 			.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
 		let _persistence_guard = PersistenceNotifierGuard::notify_on_drop(self);
@@ -9193,7 +9193,7 @@ where
 				let context = OffersContext::InboundPayment {
 					payment_hash: invoice.payment_hash(),
 				};
-				let reply_paths = self.create_blinded_paths(context)
+				let reply_paths = self.create_blinded_paths(MessageContext::Offers(context))
 					.map_err(|_| Bolt12SemanticError::MissingPaths)?;
 
 				let mut pending_offers_messages = self.pending_offers_messages.lock().unwrap();
@@ -9340,7 +9340,7 @@ where
 		if absolute_expiry.unwrap_or(Duration::MAX) <= max_short_lived_absolute_expiry {
 			self.create_compact_blinded_paths(context)
 		} else {
-			self.create_blinded_paths(context)
+			self.create_blinded_paths(MessageContext::Offers(context))
 		}
 	}
 
@@ -9361,7 +9361,7 @@ where
 	/// [`MessageRouter::create_blinded_paths`].
 	///
 	/// Errors if the `MessageRouter` errors.
-	fn create_blinded_paths(&self, context: OffersContext) -> Result<Vec<BlindedMessagePath>, ()> {
+	fn create_blinded_paths(&self, context: MessageContext) -> Result<Vec<BlindedMessagePath>, ()> {
 		let recipient = self.get_our_node_id();
 		let secp_ctx = &self.secp_ctx;
 
@@ -9374,7 +9374,7 @@ where
 			.collect::<Vec<_>>();
 
 		self.router
-			.create_blinded_paths(recipient, MessageContext::Offers(context), peers, secp_ctx)
+			.create_blinded_paths(recipient, context, peers, secp_ctx)
 			.and_then(|paths| (!paths.is_empty()).then(|| paths).ok_or(()))
 	}