Fix overflow in awaiting_pong_timer... with too many peers

If we have more than
127 / `MAX_BUFFER_DRAIN_TICK_INTERVALS_PER_PEER` (31) peers,
`awaiting_pong_timer_tick_intervals` can overflow before we hit
the limit. This isn't super harmful, we'll still disconnect peers
as long as they don't send *any* messages between two pings, but it
does cause us to not disconnect peers which are extremely slow in
responding to messages, e.g. because they are overloaded.

Author: TheBlueMatt

lightning/src/ln/peer_handler.rs

@@ -416,7 +416,7 @@ struct Peer {
 	sync_status: InitSyncTracker,
 
 	msgs_sent_since_pong: usize,
-	awaiting_pong_timer_tick_intervals: i8,
+	awaiting_pong_timer_tick_intervals: i64,
 	received_message_since_timer_tick: bool,
 	sent_gossip_timestamp_filter: bool,