[NET]: Add const markers to various variables.

the patch below marks various variables const in net/; the goal is to
move them to the .rodata section so that they can't false-share
cachelines with things that get written to, as well as potentially
helping gcc a bit with optimisations.  (these were found using a gcc
patch to warn about such variables)

Signed-off-by: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_semantics.c

@@ -83,7 +83,7 @@ for (nhsel=0; nhsel < 1; nhsel++)
 #define endfor_nexthops(fi) }
 
 
-static struct 
+static const struct 
 {
 	int	error;
 	u8	scope;