kernel: export switch_generic_set_link() symbol

This fixes:
ERROR: "switch_generic_set_link" [drivers/net/phy/b53/b53_common.ko] undefined!

At some point all packages for swconfig drivers were dropped and targets
were meant to have them built into kernels. It seems b53 (re-)gained its
kmod-switch-bcm53xx however and b53 needs to be built as module.

Fixes: b2cfed48f626 ("Revert "swconfig: fix Broadcom b53 support"")
Signed-off-by: Rafał Miłecki <[email protected]>

target/linux/generic/files/drivers/net/phy/swconfig.c

@@ -1222,6 +1222,7 @@ switch_generic_set_link(struct switch_dev *dev, int port,
 
 	return 0;
 }
+EXPORT_SYMBOL_GPL(switch_generic_set_link);
 
 static int __init
 swconfig_init(void)