igb: make a few local functions static

Clean up a few sparse warnings, these following
functions can be made static:

drivers/net/ethernet/intel/igb/igb_main.c: warning: symbol
  'igb_add_mac_filter' was not declared. Should it be static?
drivers/net/ethernet/intel/igb/igb_main.c: warning: symbol
  'igb_del_mac_filter' was not declared. Should it be static?
drivers/net/ethernet/intel/igb/igb_main.c: warning: symbol
  'igb_set_vf_mac_filter' was not declared. Should it be static?
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -6469,7 +6469,7 @@ static void igb_set_default_mac_filter(struct igb_adapter *adapter)
 	igb_rar_set_index(adapter, 0);
 }
 
-int igb_add_mac_filter(struct igb_adapter *adapter, const u8 *addr,
+static int igb_add_mac_filter(struct igb_adapter *adapter, const u8 *addr,
 			      const u8 queue)
 {
 	struct e1000_hw *hw = &adapter->hw;
@@ -6499,7 +6499,7 @@ int igb_add_mac_filter(struct igb_adapter *adapter, const u8 *addr,
 	return -ENOSPC;
 }
 
-int igb_del_mac_filter(struct igb_adapter *adapter, const u8 *addr,
+static int igb_del_mac_filter(struct igb_adapter *adapter, const u8 *addr,
 			      const u8 queue)
 {
 	struct e1000_hw *hw = &adapter->hw;
@@ -6552,7 +6552,7 @@ static int igb_uc_unsync(struct net_device *netdev, const unsigned char *addr)
 	return 0;
 }
 
-int igb_set_vf_mac_filter(struct igb_adapter *adapter, const int vf,
+static int igb_set_vf_mac_filter(struct igb_adapter *adapter, const int vf,
 				 const u32 info, const u8 *addr)
 {
 	struct pci_dev *pdev = adapter->pdev;