net/bnxt: fix crash in xstats get

We would hit a segfault in bnxt_dev_xstats_get_op() if xstats argument
is NULL, Check if the argument is NULL and return appropriately.

Fixes: bfb9c2260b ("net/bnxt: support xstats get/reset")
Cc: stable@dpdk.org

Signed-off-by: Ajit Khaparde <ajit.khaparde@broadcom.com>
Reviewed-by: Andy Gospodarek <gospo@broadcom.com>

drivers/net/bnxt/bnxt_stats.c

@@ -468,6 +468,9 @@ int bnxt_dev_xstats_get_op(struct rte_eth_dev *eth_dev,
 	if (rc)
 		return rc;
 
+	if (xstats == NULL)
+		return 0;
+
 	memset(xstats, 0, sizeof(*xstats));
 
 	bnxt_hwrm_port_qstats(bp);