GPS: Performance improvment for U-Blox hardware (#2574)

* Add proper configuration procedure for U-Blox modules

* More human friendly getACK

* Fix checksum calculation and payload

* GPS: move unsigned int check

* Introduce UBX protocol payload checksuming

* Fix missed checksums calculation for UBX-CFG-CFG

src/gps/GPS.h

@@ -139,6 +139,9 @@ class GPS : private concurrency::OSThread
     /// always returns 0 to indicate okay to sleep
     int prepareDeepSleep(void *unused);
 
+    // Calculate checksum
+    void UBXChecksum(byte *message, size_t length);
+
     /**
      * Switch the GPS into a mode where we are actively looking for a lock, or alternatively switch GPS into a low power mode
      *
@@ -179,4 +182,4 @@ class GPS : private concurrency::OSThread
 // Returns the new instance or null if the GPS is not present.
 GPS *createGps();
 
-extern GPS *gps;
+extern GPS *gps;