ixgbe: DCB: enable RSS to be used with DCB

RSS had previously been disabled when DCB was enabled because
DCB was single queued per traffic class. Now that DCB implements
multiple Tx/Rx rings per traffic class enable RSS.

Here RSS hashes across the queues in the traffic class.

Signed-off-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Ross Brattain <ross.b.brattain.@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>