Fix: prevent lfs_mountroot() from using a network device as root.
Important for net-booting of kernels which have LFS in their config,
preventing a null-pointer dereference and a crash.

Index: sys/ufs/lfs/lfs_vfsops.c
===================================================================
RCS file: /cvsroot/syssrc/sys/ufs/lfs/lfs_vfsops.c,v
retrieving revision 1.36
retrieving revision 1.38
diff -u -r1.36 -r1.38
--- lfs_vfsops.c	1999/09/03 22:48:51	1.36
+++ lfs_vfsops.c	1999/09/08 08:29:45	1.38
@@ -1,4 +1,4 @@
-/*	$NetBSD: lfs_vfsops.c,v 1.36 1999/09/03 22:48:51 perseant Exp $	*/
+/*	$NetBSD: lfs_vfsops.c,v 1.38 1999/09/08 08:29:45 augustss Exp $	*/
 
 /*-
  * Copyright (c) 1999 The NetBSD Foundation, Inc.
@@ -82,6 +82,7 @@
 #include <sys/vnode.h>
 #include <sys/mount.h>
 #include <sys/buf.h>
+#include <sys/device.h>
 #include <sys/mbuf.h>
 #include <sys/file.h>
 #include <sys/disklabel.h>
@@ -164,6 +165,11 @@
 	struct proc *p = curproc;	/* XXX */
 	int error;
 	
+	if (root_device->dv_class != DV_DISK)
+		return (ENODEV);
+
+	if (rootdev == NODEV)
+	  	return (ENODEV);
 	/*
 	 * Get vnodes for swapdev and rootdev.
 	 */