net: cavium: change NET_VENDOR_CAVIUM to bool

CONFIG_NET_VENDOR_CAVIUM is only used to hide/show config options and to
include subdirectories in the build, so it doesn't make sense to make it
tristate.

Signed-off-by: Andreas Schwab <schwab@suse.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/ethernet/cavium/Kconfig

@@ -3,7 +3,7 @@
 #
 
 config NET_VENDOR_CAVIUM
-	tristate "Cavium ethernet drivers"
+	bool "Cavium ethernet drivers"
 	depends on PCI
 	default y
 	---help---