v4l2src: preserve features when fixating caps
The caps features were lost when sorting caps structures in gst_v4l2src_fixate(). This was breaking alternate as GST_CAPS_FEATURE_FORMAT_INTERLACED was removed from the caps.
The caps features were lost when sorting caps structures in gst_v4l2src_fixate(). This was breaking alternate as GST_CAPS_FEATURE_FORMAT_INTERLACED was removed from the caps.