ixgbe: make __ixgbe_setup_tc static

This function is only used in ixgbe_main.c
Resolves a "missing prototype" warning when building the driver with W=1

Reported-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Emil Tantilov <emil.s.tantilov@intel.com>
Acked-by: John Fastabend <john.r.fastabend@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

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

@@ -8376,8 +8376,8 @@ err_out:
 	return -EINVAL;
 }
 
-int __ixgbe_setup_tc(struct net_device *dev, u32 handle, __be16 proto,
-		     struct tc_to_netdev *tc)
+static int __ixgbe_setup_tc(struct net_device *dev, u32 handle, __be16 proto,
+			    struct tc_to_netdev *tc)
 {
 	struct ixgbe_adapter *adapter = netdev_priv(dev);