i40evf: hide unused variable

On architectures with larger pages, we get a warning about an unused variable:

drivers/net/ethernet/intel/i40evf/i40evf_main.c: In function 'i40evf_configure_rx':
drivers/net/ethernet/intel/i40evf/i40evf_main.c:690:21: error: unused variable 'netdev' [-Werror=unused-variable]

This moves the declaration into the #ifdef to avoid the warning.

Fixes: dab86afdbbd1 ("i40e/i40evf: Change the way we limit the maximum frame size for Rx")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/i40evf/i40evf_main.c

@@ -694,13 +694,14 @@ static void i40evf_configure_tx(struct i40evf_adapter *adapter)
 static void i40evf_configure_rx(struct i40evf_adapter *adapter)
 {
 	unsigned int rx_buf_len = I40E_RXBUFFER_2048;
-	struct net_device *netdev = adapter->netdev;
 	struct i40e_hw *hw = &adapter->hw;
 	int i;
 
 	/* Legacy Rx will always default to a 2048 buffer size. */
 #if (PAGE_SIZE < 8192)
 	if (!(adapter->flags & I40EVF_FLAG_LEGACY_RX)) {
+		struct net_device *netdev = adapter->netdev;
+
 		/* For jumbo frames on systems with 4K pages we have to use
 		 * an order 1 page, so we might as well increase the size
 		 * of our Rx buffer to make better use of the available space