ionic: keep users rss hash across lif reset

If the user has specified their own RSS hash key, don't
lose it across queue resets such as DOWN/UP, MTU change,
and number of channels change.  This is fixed by moving
the key initialization to a little earlier in the lif
creation.

Also, let's clean up the RSS config a little better on
the way down by setting it all to 0.

Fixes: aa319881 ("ionic: Add RSS support")
Signed-off-by: Shannon Nelson <snelson@pensando.io>
Signed-off-by: David S. Miller <davem@davemloft.net>