ice: Check for q_vector when stopping rings

There is a gap in time between a VF reset, which sets the q_vector to
NULL, and the VF requesting mapping of the q_vectors. If
ice_vsi_stop_tx_rings() is called during this time, a NULL pointer
dereference is encountered. Add a check in ice_vsi_stop_tx_rings()
to ensure the q_vector is set to avoid this situation from occurring.
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>
Signed-off-by: Anirudh Venkataramanan <anirudh.venkataramanan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ice/ice_lib.c

@@ -1908,7 +1908,8 @@ int ice_vsi_stop_tx_rings(struct ice_vsi *vsi, enum ice_disq_rst_src rst_src,
 	ice_for_each_txq(vsi, i) {
 		u16 v_idx;
 
-		if (!vsi->tx_rings || !vsi->tx_rings[i]) {
+		if (!vsi->tx_rings || !vsi->tx_rings[i] ||
+		    !vsi->tx_rings[i]->q_vector) {
 			err = -EINVAL;
 			goto err_out;
 		}