use CEREG first for BG96

I refered TinyGsmClientSaraR4.h for this patch.

src/TinyGsmClientBG96.h

@@ -235,8 +235,17 @@ class TinyGsmBG96 : public TinyGsmModem<TinyGsmBG96>,
    */
  public:
   RegStatus getRegistrationStatus() {
+    // Check first for EPS registration
+    RegStatus epsStatus = (RegStatus)getRegistrationStatusXREG("CEREG");
+
+    // If we're connected on EPS, great!
+    if (epsStatus == REG_OK_HOME || epsStatus == REG_OK_ROAMING) {
+      return epsStatus;
+    } else {
+      // Otherwise, check generic network status
       return (RegStatus)getRegistrationStatusXREG("CREG");
     }
+  }
 
  protected:
   bool isNetworkConnectedImpl() {