hostapd: Add a config option to control beaconing

hostapd: Add a config option to control beaconing

In a AP/STA concurrent setup, if the STA interface is continually
scanning, trying to connect to a network, the AP interface
is basically broken since beaconing would be erratic.

This option can be used in a WDS setup where one AP acts as a
Client/AP-Repeater. The Repeater AP interface has to start beaconing
only after the Client interface has established a WDS link with the
"Root AP".

Signed-hostap: Sujith Manoharan <c_manoha@qca.qualcomm.com>