[ATALK]: Make CONFIG_DEV_APPLETALK a tristate.

Otherwise we allow building appletalk drivers in-kernel when
CONFIG_ATALK is modular.  That doesn't work because these drivers use
symbols such as "alloc_talkdev" which is exported from code built
by CONFIG_ATALK.

Noticed by Toralf Förster.
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/net/appletalk/Kconfig

@@ -29,7 +29,7 @@ config ATALK
 	  even politically correct people are allowed to say Y here.
 
 config DEV_APPLETALK
-	bool "Appletalk interfaces support"
+	tristate "Appletalk interfaces support"
 	depends on ATALK
 	help
 	  AppleTalk is the protocol that Apple computers can use to communicate