doc: elaborate on release notes wrt netmasks

Author: vasild

doc/release-notes.md

@@ -141,7 +141,8 @@ Updated settings
 
 - Netmasks that contain 1-bits after 0-bits (the 1-bits are not contiguous on
   the left side, e.g. 255.0.255.255) are no longer accepted. They are invalid
-  according to RFC 4632.
+  according to RFC 4632. Netmasks are used in the `-rpcallowip` and `-whitelist`
+  configuration options and in the `setban` RPC. (#19628)
 
 Changes to Wallet or GUI related settings can be found in the GUI or Wallet  section below.