Add an UPDATING message for r342286.

UPDATING

@@ -31,6 +31,14 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 13.x IS SLOW:
 	disable the most expensive debugging functionality run
 	"ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20181220:
+	r342286 modifies the NFSv4 server so that it obeys vfs.nfsd.nfs_privport
+	in the same as it is applied to NFSv2 and 3.  This implies that NFSv4
+	servers that have vfs.nfsd.nfs_privport set will only allow mounts
+	from clients using a reserved port#. Since both the FreeBSD and Linux
+	NFSv4 clients use reserved port#s by default, this should not affect
+	most NFSv4 mounts.
+
 20181219:
 	The XLP config has been removed. We can't support 64-bit atomics in this
 	kernel because it is running in 32-bit mode. XLP users must transition