ixgbe: Drop unnecessary call to rcu_barrier

The ixgbe driver hasn't used call_rcu to free the rings for some time now.
Since that is the case the call to rcu_barrier can be dropped since calls
to kfree_rcu don't require it.
Signed-off-by: Alexander Duyck <alexander.h.duyck@redhat.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

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

@@ -9038,8 +9038,6 @@ static void __exit ixgbe_exit_module(void)
 	pci_unregister_driver(&ixgbe_driver);
 
 	ixgbe_dbg_exit();
-
-	rcu_barrier(); /* Wait for completion of call_rcu()'s */
 }
 
 #ifdef CONFIG_IXGBE_DCA