[NET]: Make NETDEVICES depend on NET.

Enabling drivers from "Devices > Networking" (in menuconfig), for 
example SLIP and/or PLIP, throws link time errors when CONFIG_NET itself 
is =n. Have CONFIG_NETDEVICES depend on CONFIG_NET.
Signed-off-by: Jan Engelhardt <jengelh@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/Kconfig

@@ -5,6 +5,7 @@
 
 menuconfig NETDEVICES
 	default y if UML
+	depends on NET
 	bool "Network device support"
 	---help---
 	  You can say N here if you don't intend to connect your Linux box to