igb: Fix NULL pointer dereference in ethtool loopback test

The igb driver currently causes a NULL pointer dereference when executing
the ethtool loopback test. This occurs because there is no associated
q_vector for the test ring when it is set up, as interrupts are typically
not added to the test rings.

Since commit 5ef44b3c removed the napi_id assignment in
__xdp_rxq_info_reg(), there is no longer a need to pass a napi_id to it.
Therefore, simply use 0 as the last parameter.

Fixes: 2c619601 ("igb: Add AF_XDP zero-copy Rx support")
Reviewed-by: Aleksandr Loktionov <aleksandr.loktionov@intel.com>
Reviewed-by: Joe Damato <joe@dama.to>
Signed-off-by: Tianyu Xu <tianyxu@cisco.com>
Reviewed-by: Paul Menzel <pmenzel@molgen.mpg.de>
Tested-by: Rinitha S <sx.rinitha@intel.com> (A Contingent worker at Intel)
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>