mesh: Enable mesh HT mode

mesh: Enable mesh HT mode

Add a new option "mesh_ht_mode" that specifies the HT mode for the
mesh, with this option on, mesh beacons, actions frames, and probe
responses with include the appropriate HT information elements.

[original implementation by Chun-Yeow Yeoh <yeohchunyeow@gmail.com>]
[some fixes by Masashi Honma <masashi.honma@gmail.com>]
Signed-off-by: Ashok Nagarajan <ashok.dragon@gmail.com>
Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: Jason Mobarak <x@jason.mobarak.name>