[IPV4]: fix IP_FIB_HASH kconfig warning

This patch fixes the following kconfig warning:
  net/ipv4/Kconfig:92:warning: defaults for choice values not supported
Signed-off-by: NAdrian Bunk <bunk@stusta.de>
Signed-off-by: NAndrew Morton <akpm@osdl.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

net/ipv4/Kconfig

@@ -54,9 +54,9 @@ config IP_ADVANCED_ROUTER
 choice 
 	prompt "Choose IP: FIB lookup algorithm (choose FIB_HASH if unsure)"
 	depends on IP_ADVANCED_ROUTER
-	default IP_FIB_HASH
+	default ASK_IP_FIB_HASH
 
-config IP_FIB_HASH
+config ASK_IP_FIB_HASH
 	bool "FIB_HASH"
 	---help---
 	Current FIB is very proven and good enough for most users.
@@ -82,12 +82,8 @@ config IP_FIB_TRIE
        
 endchoice
 
-# If the user does not enable advanced routing, he gets the safe
-# default of the fib-hash algorithm.
 config IP_FIB_HASH
-	bool
-	depends on !IP_ADVANCED_ROUTER
-	default y
+	def_bool ASK_IP_FIB_HASH || !IP_ADVANCED_ROUTER
 
 config IP_MULTIPLE_TABLES
 	bool "IP: policy routing"