MFC rev 1.49: Don't create memory backed file systems with soft-updates

enabled, it's pointless and potentially dangerous.

PR:		conf/85558
Submitted by:	Ralf Wenk <RZ dash FreeBSD0605 at hs dash karlsruhe dot de>

etc/rc.initdiskless

@@ -145,7 +145,7 @@ chkerr() {
 # Create a generic memory disk
 #
 mount_md() {
-    /sbin/mdmfs -i 4096 -s $1 -M md $2
+    /sbin/mdmfs -S -i 4096 -s $1 -M md $2
 }
 
 # Create the memory filesystem if it has not already been created