onedrive: make --onedrive-delta quicker when not listing from the drive root

Rclone always asked for the delta listing of the whole drive and threw
away the items which weren't under the directory being listed.

The delta API now works on any folder, so ask for the delta listing of
the directory being listed instead, falling back to listing from the
root of the drive for drives which only support delta there.

docs/content/onedrive.md

@@ -326,10 +326,11 @@ This can be useful with `rclone mount` and [rclone rc vfs/refresh
 recursive=true](/rc/#vfs-refresh)) to very quickly fill the mount with
 information about all the files.
 
-The API used for the recursive listing (`ListR`) only supports listing
-from the root of the drive. This will become increasingly inefficient
-the further away you get from the root as rclone will have to discard
-files outside of the directory you are using.
+Rclone asks for the delta listing of the directory being listed. Some
+drives only support delta listings from the root of the drive, in
+which case rclone lists the whole drive and discards the files outside
+of the directory you are using, which is increasingly inefficient the
+further away from the root you get.
 
 Some commands (like `rclone lsf -R`) will use `ListR` by default - you
 can turn this off with `--disable ListR` if you need to.