ixgbe: set queue0 for srrctl configuration correctly for DCB

The current configuration is not setting queue 0 correctly for DCB
configurations.  As a result unconfigured queues are being used to setup
the SRRCTL register rx buffer len sizes.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>