Fixed breakage of binary compatibility of the kern.clockrate sysctl in

sys/time.h rev.1.53, etc.  Zero out the entire struct clkinfo and not
just the new spare part of it so that there is no possibility of leaking
kernel stack context to userland.

sys/kern/kern_clock.c

@@ -479,6 +479,7 @@ sysctl_kern_clockrate(SYSCTL_HANDLER_ARGS)
 	/*
 	 * Construct clockinfo structure.
 	 */
+	bzero(&clkinfo, sizeof(clkinfo));
 	clkinfo.hz = hz;
 	clkinfo.tick = tick;
 	clkinfo.profhz = profhz;

sys/sys/time.h

@@ -255,6 +255,7 @@ struct itimerval {
 struct clockinfo {
 	int	hz;		/* clock frequency */
 	int	tick;		/* micro-seconds per hz tick */
+	int	spare;
 	int	stathz;		/* statistics clock frequency */
 	int	profhz;		/* profiling clock frequency */
 };