igb: inline igb_maybe_stop_tx

igb_maybe_stop_tx() is extremely small and appears in several spots in
the tx hotpath. This change inlines the function for a possible
performance boost.
Signed-off-by: NNicholas Nunley <nicholasx.d.nunley@intel.com>
Signed-off-by: NJeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

drivers/net/igb/igb_main.c

@@ -3758,7 +3758,7 @@ static int __igb_maybe_stop_tx(struct igb_ring *tx_ring, int size)
 	return 0;
 }
 
-static int igb_maybe_stop_tx(struct igb_ring *tx_ring, int size)
+static inline int igb_maybe_stop_tx(struct igb_ring *tx_ring, int size)
 {
 	if (igb_desc_unused(tx_ring) >= size)
 		return 0;