MEDIUM: htx: Improve htx_xfer API to not count HTX meta-data

MEDIUM: htx: Improve htx_xfer API to not count HTX meta-data

This patch add the ability to the htx_xfer() function to transfer data
without acounting the meta-data. By default, the <count> variable includes
the meta-data. But by setting the flag HTX_XFER_NO_METADATA, It is possible
to transfer HTX blocks without count meta-data. In that case, <count> will
not contain the blocks meta-data and the return value will not include them.