Propagate extent_bytes change to autotrim thread

The autotrim thread only reads zfs_trim_extent_bytes_min and
zfs_trim_extent_bytes_max variable only on thread start.  We
should check for parameter changes during thread execution to
allow parameter changes take effect without needing to disable
then restart the autotrim.

Reviewed-by: Brian Behlendorf <[email protected]>
Signed-off-by: Václav Skála <[email protected]>
Closes openzfs#14077

module/zfs/vdev_trim.c

@@ -1188,12 +1188,11 @@ vdev_autotrim_thread(void *arg)
 	mutex_exit(&vd->vdev_autotrim_lock);
 	spa_config_enter(spa, SCL_CONFIG, FTAG, RW_READER);
 
-	uint64_t extent_bytes_max = zfs_trim_extent_bytes_max;
-	uint64_t extent_bytes_min = zfs_trim_extent_bytes_min;
-
 	while (!vdev_autotrim_should_stop(vd)) {
 		int txgs_per_trim = MAX(zfs_trim_txg_batch, 1);
 		boolean_t issued_trim = B_FALSE;
+		uint64_t extent_bytes_max = zfs_trim_extent_bytes_max;
+		uint64_t extent_bytes_min = zfs_trim_extent_bytes_min;
 
 		/*
 		 * All of the metaslabs are divided in to groups of size