qsap: Add APIs to control and manage bridge interface.

This adds APIs to trigger create, delete, interface up and interface
down commands on bridge interface.
It uses following IOCTLs for sending command to linux kernel:
Add bridge iface: SIOCBRADDBR
Remove bridge iface: SIOCBRDELBR
Mark iface up/down: SIOCGIFFLAGS

CRs-Fixed: 2080924
Change-Id: I3d34dc16e9ca82dc4b550cbc83fa4120c80ad54c

softap/sdk/qsap_api.h

@@ -603,6 +603,7 @@ int qsap_get_mode(s32 *pmode);
 int qsap_prepare_softap(void);
 int qsap_unprepare_softap(void);
 int qsap_is_fst_enabled(void);
+int qsap_control_bridge(int argc, char ** argv);
 
 #if __cplusplus
 };  // extern "C"