i40e: Use correct flag to enable egress traffic for unicast promisc

Albeit, we usually set true promiscuous mode for both multicast and
unicast at the same time - however, it is possible to set it
individually, so using allmulti flag which is only for allmulticast might
caused unwanted behavior in mirroring egress traffic promiscuous for
unicast in VF.

Signed-off-by: Akeem G Abodunrin <akeem.g.abodunrin@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>