v4l2: check device caps
Created by: pH5
Recent kernels add metadata devices next to UVC capture devices. These have the V4L2_CAP_DEVICE_CAPS and V4L2_CAP_VIDEO_CAPTURE flags set in capabilities, but V4L2_CAP_VIDEO_CAPTURE unset in device_caps. Check device caps as well to determine video capture capability. Fixes #37 (closed).