ixgbe: ixgbe_fwd_ring_down needs to be static

When compiling with -Wstrict-prototypes gcc catches a static
I missed.

./ixgbe_main.c:4254: warning: no previous prototype for 'ixgbe_fwd_ring_down'
Reported-by: NPhillip Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: NJohn Fastabend <john.r.fastabend@intel.com>
Tested-by: NPhil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/ixgbe/ixgbe_main.c

@@ -4251,7 +4251,7 @@ static void ixgbe_disable_fwd_ring(struct ixgbe_fwd_adapter *vadapter,
 	rx_ring->l2_accel_priv = NULL;
 }
 
-int ixgbe_fwd_ring_down(struct net_device *vdev,
+static int ixgbe_fwd_ring_down(struct net_device *vdev,
 			       struct ixgbe_fwd_adapter *accel)
 {
 	struct ixgbe_adapter *adapter = accel->real_adapter;