APM: added RSSI to RC_CHANNELS_RAW as well

and prevent double read

ArduPlane/ArduPlane.pde

@@ -462,6 +462,10 @@ static int16_t airspeed_nudge_cm;
 // 0-(throttle_max - throttle_cruise) : throttle nudge in Auto mode using top 1/2 of throttle stick travel
 static int16_t throttle_nudge = 0;
 
+// receiver RSSI
+static uint8_t receiver_rssi;
+
+
 ////////////////////////////////////////////////////////////////////////////////
 // Ground speed
 ////////////////////////////////////////////////////////////////////////////////
@@ -880,6 +884,8 @@ static void medium_loop()
         }
 #endif
 
+        read_receiver_rssi();
+
         // Read altitude from sensors
         // ------------------
         update_alt();

ArduPlane/GCS_Mavlink.pde

@@ -301,7 +301,7 @@ static void NOINLINE send_servo_out(mavlink_channel_t chan)
         0,
         0,
         0,
-        receiver_rssi());
+        receiver_rssi);
 }
 
 static void NOINLINE send_radio_in(mavlink_channel_t chan)
@@ -318,7 +318,7 @@ static void NOINLINE send_radio_in(mavlink_channel_t chan)
         g.rc_6.radio_in,
         g.rc_7.radio_in,
         g.rc_8.radio_in,
-        receiver_rssi());
+        receiver_rssi);
 }
 
 static void NOINLINE send_radio_out(mavlink_channel_t chan)

ArduPlane/sensors.pde

@@ -56,17 +56,12 @@ static void read_battery(void)
 }
 
 
-// return receiver RSSI as an 8 bit number for MAVLink
+// read the receiver RSSI as an 8 bit number for MAVLink
 // RC_CHANNELS_SCALED message
-uint8_t receiver_rssi(void)
+void read_receiver_rssi(void)
 {
 #if RECEIVER_RSSI_PIN != -1
     float ret = RSSI_pin.read();
-    if (ret >= 255) {
-        return 255;
-    }
-    return (uint8_t)ret;
-#else
-    return 0;
+    receiver_rssi = constrain(ret, 0, 255);
 #endif
 }