Add mesh_group_{add,remove} control interface commands

Add mesh_group_{add,remove} control interface commands

Parse MESH_GROUP_ADD/REMOVE commands on ctrl interface and call
wpa_supplicant routines. These commands are used to start or
join and leave a mesh network.

The mesh id is given in the configuration file, therefore there is
no need to scan before joining a mesh network. We reuse the
connect_without_scan construct used by P2P for that same purpose.

Signed-off-by: Javier Cardona <javier@cozybit.com>
Signed-off-by: Javier Lopez <jlopex@gmail.com>