net: mvneta: Don't force-set the offloading flag

The qopt->hw flag is set by the TC code according to the offloading mode
asked by user. Don't force-set it in the driver, but instead read it to
make sure we do what's asked.

Signed-off-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Signed-off-by: David S. Miller <davem@davemloft.net>