net/ncsi: fix ncsi_vlan_rx_{add,kill}_vid references

We get a new link error in allmodconfig kernels after ftgmac100
started using the ncsi helpers:

ERROR: "ncsi_vlan_rx_kill_vid" [drivers/net/ethernet/faraday/ftgmac100.ko] undefined!
ERROR: "ncsi_vlan_rx_add_vid" [drivers/net/ethernet/faraday/ftgmac100.ko] undefined!

Related to that, we get another error when CONFIG_NET_NCSI is disabled:

drivers/net/ethernet/faraday/ftgmac100.c:1626:25: error: 'ncsi_vlan_rx_add_vid' undeclared here (not in a function); did you mean 'ncsi_start_dev'?
drivers/net/ethernet/faraday/ftgmac100.c:1627:26: error: 'ncsi_vlan_rx_kill_vid' undeclared here (not in a function); did you mean 'ncsi_vlan_rx_add_vid'?

This fixes both problems at once, using a 'static inline' stub helper
for the disabled case, and exporting the functions when they are present.

Fixes: 51564585 ("ftgmac100: Support NCSI VLAN filtering when available")
Fixes: 21acf630 ("net/ncsi: Configure VLAN tag filter")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/ncsi.h

@@ -36,6 +36,16 @@ int ncsi_start_dev(struct ncsi_dev *nd);
 void ncsi_stop_dev(struct ncsi_dev *nd);
 void ncsi_unregister_dev(struct ncsi_dev *nd);
 #else /* !CONFIG_NET_NCSI */
+static inline int ncsi_vlan_rx_add_vid(struct net_device *dev, __be16 proto, u16 vid)
+{
+	return -EINVAL;
+}
+
+static inline int ncsi_vlan_rx_kill_vid(struct net_device *dev, __be16 proto, u16 vid)
+{
+	return -EINVAL;
+}
+
 static inline struct ncsi_dev *ncsi_register_dev(struct net_device *dev,
 					void (*notifier)(struct ncsi_dev *nd))
 {

net/ncsi/ncsi-manage.c

@@ -1453,6 +1453,7 @@ int ncsi_vlan_rx_add_vid(struct net_device *dev, __be16 proto, u16 vid)
 
 	return found ? ncsi_process_next_channel(ndp) : 0;
 }
+EXPORT_SYMBOL_GPL(ncsi_vlan_rx_add_vid);
 
 int ncsi_vlan_rx_kill_vid(struct net_device *dev, __be16 proto, u16 vid)
 {
@@ -1491,6 +1492,7 @@ int ncsi_vlan_rx_kill_vid(struct net_device *dev, __be16 proto, u16 vid)
 
 	return found ? ncsi_process_next_channel(ndp) : 0;
 }
+EXPORT_SYMBOL_GPL(ncsi_vlan_rx_kill_vid);
 
 struct ncsi_dev *ncsi_register_dev(struct net_device *dev,
 				   void (*handler)(struct ncsi_dev *ndev))