net: mvpp2: check ethtool sets the Tx ring size is to a valid min value

net: mvpp2: check ethtool sets the Tx ring size is to a valid min value

This patch fixes the Tx ring size checks when using ethtool, by adding
an extra check in the PPv2 check_ringparam_valid helper. The Tx ring
size cannot be set to a value smaller than the minimum number of
descriptors needed for TSO.

Fixes: 1d17db08c056 ("net: mvpp2: limit TSO segments and use stop/wake thresholds")
Suggested-by: Yan Markman <[email protected]>
Signed-off-by: Antoine Tenart <[email protected]>
Signed-off-by: David S. Miller <[email protected]>