net/mlx5e: Protect en header file from redefinitions

add ifndef to en.h. needed for upcoming vxlan patchset.
Signed-off-by: Matthew Finlay <matt@mellanox.com>
Signed-off-by: Saeed Mahameed <saeedm@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/mellanox/mlx5/core/en.h

 /*
- * Copyright (c) 2015, Mellanox Technologies. All rights reserved.
+ * Copyright (c) 2015-2016, Mellanox Technologies. All rights reserved.
  *
  * This software is available to you under a choice of one of two
  * licenses.  You may choose to be licensed under the terms of the GNU
@@ -29,6 +29,8 @@
  * CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
  * SOFTWARE.
  */
+#ifndef __MLX5_EN_H__
+#define __MLX5_EN_H__
 
 #include <linux/if_vlan.h>
 #include <linux/etherdevice.h>
@@ -678,3 +680,5 @@ int mlx5e_dcbnl_ieee_setets_core(struct mlx5e_priv *priv, struct ieee_ets *ets);
 #endif
 
 u16 mlx5e_get_max_inline_cap(struct mlx5_core_dev *mdev);
+
+#endif /* __MLX5_EN_H__ */