igbvf, ixgbevf: use dev_hw_addr_random

Both igbvf and ixgbevf should set addr_assign_type to NET_ADDR_RANDOM
so udev creates persistent net rules by matching the device path.
Do this by using the dev_hw_addr_random helper function.

Signed-off-by: Stefan Assmann <sassmann@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>