Ignore calcru: runtime went backwards for vm_guest

VM's have little control over CPU speed, don't make matters worse
by constantly spaming console.

Reviewed by:	jhb
Differential Revision:	https://reviews.freebsd.org/D33902

sys/kern/kern_resource.c

@@ -1018,7 +1018,7 @@ calcru1(struct proc *p, struct rusage_ext *ruxp, struct timeval *up,
 		uu = ruxp->rux_uu;
 		su = ruxp->rux_su;
 		tu = ruxp->rux_tu;
-	} else { /* tu < ruxp->rux_tu */
+	} else if (vm_guest == VM_GUEST_NO) {  /* tu < ruxp->rux_tu */
 		/*
 		 * What happened here was likely that a laptop, which ran at
 		 * a reduced clock frequency at boot, kicked into high gear.