af_xdp: ensure at least one queue is created

Attempting to create an af_xdp interface with zerocopy where the
underlying driver didn't support it would lead to a crash due to
queue creation silently failing.

Type: fix

Signed-off-by: Joshua Roys <roysjosh@gmail.com>
Change-Id: Ifd9070b8c2b3023d71120c5cf20f7e89d04e4cb3
diff --git a/src/plugins/af_xdp/device.c b/src/plugins/af_xdp/device.c
index 30d3c95..8365a71 100644
--- a/src/plugins/af_xdp/device.c
+++ b/src/plugins/af_xdp/device.c
@@ -460,6 +460,8 @@
 	   * requested 'max'
 	   * we might create less tx queues than workers but this is ok
 	   */
+	  af_xdp_log (VLIB_LOG_LEVEL_DEBUG, ad,
+		      "create interface failed to create queue qid=%d", i);
 
 	  /* fixup vectors length */
 	  vec_set_len (ad->umem, i);
@@ -470,7 +472,8 @@
 	  ad->rxq_num = clib_min (i, rxq_num);
 	  ad->txq_num = clib_min (i, txq_num);
 
-	  if (i < rxq_num && AF_XDP_NUM_RX_QUEUES_ALL != args->rxq_num)
+	  if (i == 0 ||
+	      (i < rxq_num && AF_XDP_NUM_RX_QUEUES_ALL != args->rxq_num))
 	    {
 	      ad->rxq_num = ad->txq_num = 0;
 	      goto err1; /* failed creating requested rxq: fatal error, bailing