i40e: use minimal Tx and Rx pairs for kdump

Set the number of the MSI-X vectors to 1. When MSI-X is enabled,
it's not allowed to use more TC queue pairs than MSI-X vectors
(pf->num_lan_msix) exist. Thus the number of Tx and Rx pairs
(vsi->num_queue_pairs) will be equal to the number of MSI-X vectors,
i.e., 1.

Signed-off-by: Coiby Xu <coxu@redhat.com>
Tested-by: Dave Switzer <david.switzer@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>