Drop bzero and shove the responsibility of zeroing the kse upcall

object on to the zone allocator. It should be noted that uma_zalloc(9)
uses bzero to zero out the object so there probably wont be any
real performance benefit. If UMA grows the ability to supply
zeroed zones more efficiently in the future, we will not have to
modify all the existing consumers.

Discussed with:	rwatson,julian
MFC after:	1 week

sys/kern/kern_kse.c

@@ -73,8 +73,7 @@ upcall_alloc(void)
 {
 	struct kse_upcall *ku;
 
-	ku = uma_zalloc(upcall_zone, M_WAITOK);
-	bzero(ku, sizeof(*ku));
+	ku = uma_zalloc(upcall_zone, M_WAITOK | M_ZERO);
 	return (ku);
 }