Bound sync loops in lightning-transaction-sync

If we start syncing from an electrum or esplora server and find
that the chain moved during our sync, we reset and start fresh.
However, if that happens repeatedly, we probably shouldn't just
spin forever. Here we give up after five attempts and just hope we
can sync properly later.

Author: TheBlueMatt

lightning-transaction-sync/src/electrum.rs

@@ -102,7 +102,7 @@ where
 		let mut tip_header = tip_notification.header;
 		let mut tip_height = tip_notification.height as u32;
 
-		loop {
+		for _ in 0..5 {
 			let pending_registrations = self.queue.lock().unwrap().process_queues(&mut sync_state);
 			let tip_is_new = Some(tip_header.block_hash()) != sync_state.last_sync_hash;
 

lightning-transaction-sync/src/esplora.rs

@@ -106,7 +106,7 @@ where
 
 		let mut tip_hash = maybe_await!(self.client.get_tip_hash())?;
 
-		loop {
+		for _ in 0..5 {
 			let pending_registrations = self.queue.lock().unwrap().process_queues(&mut sync_state);
 			let tip_is_new = Some(tip_hash) != sync_state.last_sync_hash;