mac80211: Rename mesh_params to mesh_config to prepare for mesh_setup

Mesh parameters can be to setup a mesh or to configure it.
This patch renames the ambiguous name mesh_params to mesh_config
in preparation for mesh_setup.

Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>