[NETLINK]: fib_lookup() via netlink

Below is a more generic patch to do fib_lookup via netlink. For others 
we should say that we discussed this as a way to verify route selection.
It's also possible there are others uses for this.

In short the fist half of struct fib_result_nl is filled in by caller 
and netlink call fills in the other half and returns it.

In case anyone is interested there is a corresponding user app to compare 
the full routing table this was used to test implementation of the LC-trie. 

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

include/net/ip_fib.h

@@ -109,6 +109,20 @@ struct fib_result {
 #endif
 };
 
+struct fib_result_nl {
+	u32		fl_addr;   /* To be looked up*/ 
+	u32		fl_fwmark; 
+	unsigned char	fl_tos;
+	unsigned char   fl_scope;
+	unsigned char   tb_id_in;
+
+	unsigned char   tb_id;      /* Results */
+	unsigned char	prefixlen;
+	unsigned char	nh_sel;
+	unsigned char	type;
+	unsigned char	scope;
+	int             err;      
+};
 
 #ifdef CONFIG_IP_ROUTE_MULTIPATH