GPS: open the GPS serial port with a 256 byte buffer

the UBLOX needs more than 128 bytes for reliable parsing

ArduCopter/system.pde

@@ -83,7 +83,9 @@ static void init_ardupilot()
 	// GPS serial port.
 	//
 	#if GPS_PROTOCOL != GPS_PROTOCOL_IMU
-	Serial1.begin(38400, 128, 16);
+    // standard gps running. Note that we need a 256 byte buffer for some
+    // GPS types (eg. UBLOX)
+    Serial1.begin(38400, 256, 16);
 	#endif
 
 	Serial.printf_P(PSTR("\n\nInit " THISFIRMWARE

ArduPlane/system.pde

@@ -86,7 +86,7 @@ static void init_ardupilot()
 	// GPS serial port.
 	//
     // standard gps running
-    Serial1.begin(38400, 128, 16);
+    Serial1.begin(38400, 256, 16);
 
 	Serial.printf_P(PSTR("\n\nInit " THISFIRMWARE
 						 "\n\nFree RAM: %u\n"),