Use vmem_zalloc to silence allocation warning

The kmem allocation in zfs_prune_aliases() will trigger a large
allocation warning on systems with 64K pages.  Resolve this by
switching to vmem_alloc() which internally uses kvmalloc() so the
right allocator will be used based on the allocation size.

Reviewed-by: Richard Yao <richard.yao@alumni.stonybrook.edu>
Reviewed-by: Tino Reichardt <milky-zfs@mcmilk.de>
Reviewed-by: Brian Atkinson <batkinson@lanl.gov>
Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>
Closes #8491
Closes #14694

module/os/linux/zfs/zfs_vfsops.c

@@ -1192,7 +1192,7 @@ zfs_prune_aliases(zfsvfs_t *zfsvfs, unsigned long nr_to_scan)
 	int objects = 0;
 	int i = 0, j = 0;
 
-	zp_array = kmem_zalloc(max_array * sizeof (znode_t *), KM_SLEEP);
+	zp_array = vmem_zalloc(max_array * sizeof (znode_t *), KM_SLEEP);
 
 	mutex_enter(&zfsvfs->z_znodes_lock);
 	while ((zp = list_head(&zfsvfs->z_all_znodes)) != NULL) {
@@ -1228,7 +1228,7 @@ zfs_prune_aliases(zfsvfs_t *zfsvfs, unsigned long nr_to_scan)
 		zrele(zp);
 	}
 
-	kmem_free(zp_array, max_array * sizeof (znode_t *));
+	vmem_free(zp_array, max_array * sizeof (znode_t *));
 
 	return (objects);
 }