[FIB]: Reduce text size of net/ipv4/fib_trie.o

In struct tnode, we use two fields of 5 bits for 'pos' and 'bits'.
Switching to plain 'unsigned char' (8 bits) take the same space
because of compiler alignments, and reduce text size by 435 bytes
on i386.

On i386 :
$ size net/ipv4/fib_trie.o.before_patch net/ipv4/fib_trie.o
    text    data     bss     dec     hex filename
   13714       4      64   13782    35d6 net/ipv4/fib_trie.o.before
   13279       4      64   13347    3423 net/ipv4/fib_trie.o
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Acked-by: Stephen Hemminger <stephen.hemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

net/ipv4/fib_trie.c

@@ -118,8 +118,8 @@ struct leaf_info {
 struct tnode {
 	t_key key;
 	unsigned long parent;
-	unsigned short pos:5;		/* 2log(KEYLENGTH) bits needed */
-	unsigned short bits:5;		/* 2log(KEYLENGTH) bits needed */
+	unsigned char pos;		/* 2log(KEYLENGTH) bits needed */
+	unsigned char bits;		/* 2log(KEYLENGTH) bits needed */
 	unsigned short full_children;	/* KEYLENGTH bits needed */
 	unsigned short empty_children;	/* KEYLENGTH bits needed */
 	struct rcu_head rcu;