Updated example for cellular only: clearer eDRX outcome. (#1135)

The E-DRX example for cellular expects that, once E-DRX has been set, the module will emit a URC indicating the assigned E-DRX settings. This works internally on the ubxlib test system however it doesn't seem to be a reliable indication for a live network: likely it depends on the network and when the radio connection is released. So as not to confuse customers, the example is now updated to call the uCellPwrGetEDrx() API to determine the truth if the callback happens not to be called.

Thanks to elektron314 for spotting this.

example/cell/power_saving/cell_power_saving_e_drx_main.c

@@ -211,6 +211,9 @@ U_PORT_TEST_FUNCTION("[example]", "exampleCellPowerSavingEDrx")
     bool onMyRat = true;
     int32_t x = -1;
     int32_t returnCode;
+    bool eDrxOnNotOff = false;
+    int32_t eDrxSeconds = -1;
+    int32_t pagingWindowSeconds = -1;
 
     // Initialise the APIs we will need
     uPortInit();
@@ -260,9 +263,32 @@ U_PORT_TEST_FUNCTION("[example]", "exampleCellPowerSavingEDrx")
                     }
 
                     if (gEDrxSet) {
-                        uPortLog("### The E-DRX settings have been agreed.\n");
+                        uPortLog("### Callback called, the E-DRX settings"
+                                 " have been agreed.\n");
                     } else {
-                        uPortLog("### Unable to switch E-DRX on!\n");
+                        // The callback has not been called, which might
+                        // be the case, network dependent, dependent on
+                        // the timing of RRC connections being dropped
+                        // etc.; call the API instead
+                        if (uCellPwrGetEDrx(devHandle, MY_RAT,
+                                            &eDrxOnNotOff, &eDrxSeconds,
+                                            &pagingWindowSeconds) == 0) {
+                            if (eDrxOnNotOff) {
+                                uPortLog("### The E-DRX settings have been agreed");
+                                if (eDrxSeconds >= 0) {
+                                    uPortLog(", assigned E-DRX %d seconds", eDrxSeconds);
+                                }
+                                if (pagingWindowSeconds >= 0) {
+                                    uPortLog(", assigned paging window %d seconds",
+                                             pagingWindowSeconds);
+                                }
+                                uPortLog(".\n");
+                            } else {
+                                uPortLog("### Unable to switch E-DRX on!\n");
+                            }
+                        } else {
+                            uPortLog("### Unable to get assigned E-DRX!\n");
+                        }
                     }
 
                     // When finished with the network layer
@@ -295,7 +321,8 @@ U_PORT_TEST_FUNCTION("[example]", "exampleCellPowerSavingEDrx")
     uPortLog("### Done.\n");
 
 # ifndef U_CFG_CELL_DISABLE_UART_POWER_SAVING
-    // For u-blox internal testing only
+    // For u-blox internal testing only; in our test setup we
+    // can be sure that the callback should have been called
     EXAMPLE_FINAL_STATE((x < 0) || gEDrxSet);
 #  ifdef U_PORT_TEST_ASSERT
     // We don't want E-DRX on for our internal testing, so