Fix assert on SystemLayer().StartTimer call by aquiring the chipStack Lock before the call (#26200)

Author: jmartinez-silabs

src/platform/Linux/BLEManagerImpl.cpp

@@ -796,7 +796,11 @@ void BLEManagerImpl::OnDeviceScanned(BluezDevice1 * device, const chip::Ble::Chi
     }
 
     mBLEScanConfig.mBleScanState = BleScanState::kConnecting;
+
+    chip::DeviceLayer::PlatformMgr().LockChipStack();
     DeviceLayer::SystemLayer().StartTimer(kConnectTimeout, HandleConnectTimeout, mpEndpoint);
+    chip::DeviceLayer::PlatformMgr().UnlockChipStack();
+
     mDeviceScanner->StopScan();
 
     ConnectDevice(device, mpEndpoint);