doc: banman: reference past vuln due to unbounded banlist

Author: darosior

src/banman.h

@@ -54,6 +54,11 @@ class CSubNet;
 // transaction that fails a policy check and a future version changes the
 // policy check so the transaction is accepted, then that transaction could
 // cause the network to split between old nodes and new nodes.
+//
+// NOTE: previously a misbehaving peer would get banned instead of discouraged.
+// This meant a peer could unboundedly grow our in-memory map of banned ips. When
+// receiving an ADDR message we would also compare every address received to every
+// item in the map. See https://bitcoincore.org/en/2024/07/03/disclose-unbounded-banlist.
 
 class BanMan
 {