12.2 errata: document ipfw(8) issue correction

Reported by:	vsasjason at gmail . com
Differential revision:	https://reviews.freebsd.org/D28155
Sponsored by:	Rubicon Communications, LLC (netgate.com)

en_US.ISO8859-1/htdocs/releases/12.2R/errata/errata.xml

@@ -99,7 +99,10 @@
 	  where packets are not properly forwarded with multiple IP
 	  addresses bound to the same interface.</para>
 
-	<para>An Errata Notice is planned for 12.2-RELEASE.</para>
+	<para>This issue had been corrected in
+	<link
+	    xlink:href="https://www.freebsd.org/security/advisories/FreeBSD-EN-20:21.ipfw.asc">
+	  FreeBSD-EN-20:21.ipfw</link>.</para>
 
 	<para>See
 	  <link