Currently, rte_eth_dev_mac_addr_add is used by a testpmd CLI
to add a MAC address for VF. But the parameter 'pool' of this
API means the VMDq pool, not VF.
So, it's wrong to use it to add the VF MAC address.
This patch provides a new API that can be used to
add VF MAC address on i40e.
Signed-off-by: Wenzhuo Lu <wenzhuo.lu@intel.com>