GPS: added set_secondary() function

for preventing notify updates for 2nd GPS

libraries/AP_GPS/GPS.cpp

@@ -36,6 +36,7 @@ GPS::GPS(void) :
 	last_fix_time(0),
 	_have_raw_velocity(false),
     _last_gps_time(0),
+    _secondary_gps(false),
 	_idleTimer(0),
 	_status(GPS::NO_FIX),
 	_last_ground_speed_cm(0),
@@ -108,9 +109,11 @@ GPS::update(void)
         }
     }
 
+    if (!_secondary_gps) {
         // update notify with gps status
         AP_Notify::flags.gps_status = _status;
     }
+}
 
 void
 GPS::setHIL(Fix_Status fix_status,

libraries/AP_GPS/GPS.h

@@ -146,6 +146,8 @@ public:
 	// return true if the GPS supports vertical velocity values
     bool have_vertical_velocity(void) const { return _have_raw_velocity; }
 
+    void set_secondary(void) { _secondary_gps = true; }
+
 protected:
     AP_HAL::UARTDriver *_port;   ///< port the GPS is attached to
 
@@ -204,6 +206,9 @@ protected:
     // the time we got the last GPS timestamp
     uint32_t _last_gps_time;
 
+    // this is a secondary GPS, disable notify updates
+    bool _secondary_gps;
+
     // return time in seconds since GPS epoch given time components
     void _make_gps_time(uint32_t bcd_date, uint32_t bcd_milliseconds);