Suppress 'vdev_metaslab_init' memory warning

The vdev_metaslab_init() function has been observed to allocate
larger than 8k chunks.  However, they are not much larger than 8k
and it does this infrequently so it is allowed and the warning is
supressed.

module/zfs/vdev.c

@@ -833,7 +833,7 @@ vdev_metaslab_init(vdev_t *vd, uint64_t txg)
 
 	ASSERT(oldc <= newc);
 
-	mspp = kmem_zalloc(newc * sizeof (*mspp), KM_SLEEP);
+	mspp = kmem_zalloc(newc * sizeof (*mspp), KM_SLEEP | KM_NODEBUG);
 
 	if (oldc != 0) {
 		bcopy(vd->vdev_ms, mspp, oldc * sizeof (*mspp));