net: thunderx: Support to configure queue sizes from ethtool

Adds support to set Rx/Tx queue sizes from ethtool. Fixes
an issue with retrieving queue size. Also sets SQ's CQ_LIMIT
based on configured Tx queue size such that HW doesn't process
SQEs when there is no sufficient space in CQ.

Signed-off-by: Sunil Goutham <sgoutham@cavium.com>
Signed-off-by: David S. Miller <davem@davemloft.net>