drivers: net: xgene: ethtool: Add get/set_pauseparam

This patch adds get_pauseparam and set_pauseparam functions.

Signed-off-by: Iyappan Subramanian <isubramanian@apm.com>
Signed-off-by: Quan Nguyen <qnguyen@apm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>