ixgbe: only register DCA requester once

The current driver tries to re-register the DCA requester after reset and
this is not correct.  This change makes it so all we are doing is resetting
the DCA registers after reset and not re-adding the requester.

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>