wifi-base: Add new APIs to support STA+STA.

This includes following changes:
 - Declare STA_SHARED/STA_PRIMARY/STA_SECONDARY to be used for
   per station interface indication
 - Add staId to WifiConfiguration class which takes one of
   WifiManager sta identity.
 - Add new APIs to start/connect secondary station.
 - Add new IWifiNotificationCallback to announce activities of
   secondary station.
 - new config 'config_wifi_framework_secondary_sta_supported'
   to support additional station.

CRs-Fixed: 2578400
Change-Id: Ibfc72b50fa7cb4a96f933b2c1f4922b1b90b4316