wlcore: add dfs master restart calls

call wlcore_cmd_dfs_master_restart when starting
the ap on a new channel (after csa is done).

Add a new WLVIF_FLAG_BEACON_DISABLED flag to
indicate that dfs_master_restart command
is required.

Signed-off-by: Eliad Peller <eliad@wizery.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>