igc: Fix TX drops in XDP ZC

Fixes TX frame drops in AF_XDP zero copy mode when budget < 4.
xsk_tx_peek_desc() consumed TX frame and it was ignored because of
low budget. Not even AF_XDP completion was done for dropped frames.

It can be reproduced on i226 by sending 100000x 60 B frames with
launch time set to minimal IPG (672 ns between starts of frames)
on 1Gbit/s. Always 1026 frames are not sent and are missing a
completion.

Fixes: 9acf59a ("igc: Enable TX via AF_XDP zero-copy")
Signed-off-by: Zdenek Bouska <zdenek.bouska@siemens.com>
Reviewed-by: Song Yoong Siang <yoong.siang.song@intel.com>
Reviewed-by: Florian Bezdeka <florian.bezdeka@siemens.com>
Tested-by: Mor Bar-Gabay <morx.bar.gabay@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>

Author: zdenek-bouska

drivers/net/ethernet/intel/igc/igc_main.c

@@ -3042,7 +3042,7 @@ static void igc_xdp_xmit_zc(struct igc_ring *ring)
 	 * descriptors. Therefore, to be safe, we always ensure we have at least
 	 * 4 descriptors available.
 	 */
-	while (xsk_tx_peek_desc(pool, &xdp_desc) && budget >= 4) {
+	while (budget >= 4 && xsk_tx_peek_desc(pool, &xdp_desc)) {
 		struct igc_metadata_request meta_req;
 		struct xsk_tx_metadata *meta = NULL;
 		struct igc_tx_buffer *bi;