mesh: deinit or free the mesh interface to eliminate memory leak

Deinit and free the mesh interface accordingly to avoid memory leak
happened. Previous segmentation fault reported by Thomas is due to
the mesh_mpm_deinit is calling the hostapd_free_stas and this is also
called by hostapd_interface_deinit. mesh_mpm_deinit seems no longer
needed, so take this out as well.

Signed-off-by: Chun-Yeow Yeoh <yeohchunyeow@cozybit.com>
Merge pull request #6 from cozybit/yeow-fix-memory-leak

Restore the deinit and free the mesh interfaces to avoid memory leak

Thanks.