pcapng: use the Wayback Machine for the NSS key log format.

draft-ietf-opsawg-pcapng.md

@@ -2058,7 +2058,7 @@ The following is a list of Secrets Types.
 {: indent='8'}
 0x544c534b:
 : TLS Key Log. This
-  format is described at [NSS Key Log Format](https://udn.realityripple.com/docs/Mozilla/Projects/NSS/Key_Log_Format). Every line MUST be properly terminated with
+  format is described at [NSS Key Log Format](https://web.archive.org/web/20220206172425/https://developer.mozilla.org/en-US/docs/Mozilla/Projects/NSS/Key_Log_Format). Every line MUST be properly terminated with
   either carriage return and linefeed ('\r\n') or linefeed ('\n').
   Tools MUST be able to handle both line endings.
 {: vspace='0'}