v4l2: fallback on path if no SERIAL

This allows virtual cameras to be detected by Jami and be able to
stream from OBS for example.

Change-Id: Ib2554e80009876100f77fa62fd8e18bbc01ba717

src/media/video/v4l2/video_device_monitor_impl.cpp

@@ -151,7 +151,9 @@ VideoDeviceMonitorImpl::VideoDeviceMonitorImpl(VideoDeviceMonitor* monitor)
                 monitor_->addDevice(unique_name, {{{"devPath", path}}});
                 currentPathToId_.emplace(path, unique_name);
             } catch (const std::exception& e) {
-                JAMI_ERR("%s", e.what());
+                JAMI_WARN("udev: %s, fallback on path (your camera may be a fake camera)", e.what());
+                monitor_->addDevice(path, {{{"devPath", path}}});
+                currentPathToId_.emplace(path, path);
             }
         }
         udev_device_unref(dev);