Fix #26115: Setup discriminator parameter corruption (#26116)

* Fix #26115: Setup discriminator parameter corruption

The setup discriminator parameter is being passed by reference, but
by the time the block is run by dispatch, that reference points to
stack contents that have been changed.  Making a local copy of the
discriminator fixes the problem.

* Add comment explaining why we are copying the incoming discriminator.

---------

Co-authored-by: Boris Zbarsky <bzbarsky@apple.com>

src/platform/Darwin/BleConnectionDelegateImpl.mm

@@ -91,10 +91,13 @@ - (BOOL)isConnecting;
         dispatch_queue_t bleWorkQueue;
 
         void BleConnectionDelegateImpl::NewConnection(
-            Ble::BleLayer * bleLayer, void * appState, const SetupDiscriminator & deviceDiscriminator)
+            Ble::BleLayer * bleLayer, void * appState, const SetupDiscriminator & inDeviceDiscriminator)
         {
             assertChipStackLockedByCurrentThread();
 
+            // Make a copy of the device discriminator for the block to capture.
+            SetupDiscriminator deviceDiscriminator = inDeviceDiscriminator;
+
             ChipLogProgress(Ble, "%s", __FUNCTION__);
             if (!bleWorkQueue) {
                 bleWorkQueue = dispatch_queue_create(kBleWorkQueueName, DISPATCH_QUEUE_SERIAL_WITH_AUTORELEASE_POOL);