Fix nagging make_dev() warnings

[Matthew Dillon]

:Index: kern_conf.c
:===================================================================
:RCS file: /cvs/src/sys/kern/kern_conf.c,v
:retrieving revision 1.15
:diff -u -r1.15 kern_conf.c
:--- kern_conf.c	10 Sep 2006 01:26:39 -0000	1.15
:+++ kern_conf.c	26 Sep 2006 17:57:16 -0000
:@@ -114,7 +114,7 @@
:  */
: static
: cdev_t
:-hashdev(struct dev_ops *ops, int x, int y)
:+hashdev(struct dev_ops *ops, int x, int y, int allow_override)
: {
:...

    While explaining some make_dev related stuff to Victor I realized that
    I made a mistake in my commit.... I had forgotten why I had the ops check
    in there in the first place.

    The reason is that the kernel can create shadow devices which
    are supposed to be invisible to userland.  This is why the ops pointer
    is compared in hashdev().

    So we cannot just allow any ops vector mismatch to be overridden.
    I have made a followup commit which adds a flag that hashdev() can
    check for and I added a comment to the code describing the reason.

					-Matt
					Matthew Dillon 
					<dillon at xxxxxxxxxxxxx>