net/i40e/base: add function to read LPI counters

net/i40e/base: add function to read LPI counters

This change introduces new function i40e_get_lpi_counters() reading
Low Power Idle (LPI) mode counters from Energy Efficient Ethernet (EEE)
statistics. Since reading EEE statistics requires running DNL script,
function i40e_aq_run_phy_activity() able to run it, was implemented.

i40e_lpi_stat_update() was introduced as helper function for retrieving
LPI counters' values relative to given offsets.

This change also fixes order of fields in struct
i40e_aqc_run_phy_activity and introduces union in the struct
providing more descriptive names of fields depending on usage
(command or response).

Signed-off-by: Piotr Pietruszewski <piotr.pietruszewski@intel.com>
Signed-off-by: Xiaolong Ye <xiaolong.ye@intel.com>
Acked-by: Qi Zhang <qi.z.zhang@intel.com>
Acked-by: Beilei Xing <beilei.xing@intel.com>