net/i40e/base: support LLDP agent

This code implements changes necessary for LLDP Agent support.

1. Modified i40e_aq_start_lldp and i40e_aq_stop_lldp. Now Stop and Start
can also be persistent across power cycles.
2. Added new function i40e_aq_restore_lldp which restores factory
setting for LLDP Agent or gets its status.

Signed-off-by: Jaroslaw Ilgiewicz <jaroslaw.ilgiewicz@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>