net/i40e: no more initial VF MAC address

net/i40e: no more initial VF MAC address

During PF initialization, PF will generate an initial mac address
for VFs, the purpose is to help VF keep a constant mac address between
its startup/shutdown cycles. Now this is not necessary, since we already
provide an API to set VF's MAC address from PF side
(rte_pmd_i40e_set_vf_mac_addr).

Application can use this API to lock down VF's mac address.(of course this
should happen before VF init)
While without this patch, we still can use rte_pmd_i40e_set_vf_mac_addr
to overwrite the random one, but this patch align DPDK's default behavior
with Kernel PF driver's, and this help to give an identical experience
when work with kernel VF driver.

Signed-off-by: Qi Zhang <qi.z.zhang@intel.com>