vmxnet3: use static RSS key

Rather than generating a different RSS key on each boot, just use
a predetermined value that will map same flow to same value on
every device for more predictable testing. This is already done
on most hardware drivers.

Initial key value just some arbitrary bits extracted once
from /dev/random.

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: David S. Miller <davem@davemloft.net>