ANDROID: mnt: Propagate remount correctly

This switches over to propagation_next to respect
namepsace semantics.

Test: Remounting to change the options of a fs with mount based
      options should propagate to all shared copies of that mount,
      and the slaves/indirect slaves of those.
Bug: 122428178
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Change-Id: Ic35cd2782a646435689f5bedfa1f218fe4ab8254