cxgb4: Fix -Wunused-const-variable warning

If CONFIG_PCI_IOV is n, make W=1 warns:

drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c:3909:33:
 warning: ‘cxgb4_mgmt_ethtool_ops’ defined but not used [-Wunused-const-variable=]
 static const struct ethtool_ops cxgb4_mgmt_ethtool_ops = {
                                 ^~~~~~~~~~~~~~~~~~~~~~

Move it into #ifdef block to fix this.
Signed-off-by: YueHaibing <yuehaibing@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/chelsio/cxgb4/cxgb4_main.c

@@ -3894,7 +3894,6 @@ static const struct net_device_ops cxgb4_mgmt_netdev_ops = {
 	.ndo_set_vf_vlan        = cxgb4_mgmt_set_vf_vlan,
 	.ndo_set_vf_link_state	= cxgb4_mgmt_set_vf_link_state,
 };
-#endif
 
 static void cxgb4_mgmt_get_drvinfo(struct net_device *dev,
 				   struct ethtool_drvinfo *info)
@@ -3909,6 +3908,7 @@ static void cxgb4_mgmt_get_drvinfo(struct net_device *dev,
 static const struct ethtool_ops cxgb4_mgmt_ethtool_ops = {
 	.get_drvinfo       = cxgb4_mgmt_get_drvinfo,
 };
+#endif
 
 static void notify_fatal_err(struct work_struct *work)
 {