hostapd: Skip some configuration steps for mesh cases

hostapd: Skip some configuration steps for mesh cases

Modify hostapd.c logic to add checks for valid mconf data structure:

- For hostapd_setup_bss we don't need to flush old stations in case
  we're rejoining a mesh network.

- In hostapd_setup_interface_complete, we don't need to setup the
  interface until we join the mesh (same reasoning for
  hostapd_tx_queue_params).

Signed-off-by: Javier Lopez <jlopex@gmail.com>
Signed-off-by: Jason Mobarak <x@jason.mobarak.name>