v4l2object: Read driver selected interlace mode
If there was no interlace-mode field in the caps. Read back the value selected by the driver. This way, if the driver does not support progressive, then it will automatically negotiate the returned mode unless this mode is not supported by GStreamer.
This method was already used for colorimetry. Just like colorimetry, the interlace mode is not longer probed by v4l2src dues to performance issues.
Fixes #511 (closed)
Closes #511 (closed)