net/sched: fix type of htb statistics

tokens and ctokens are defined as s64 in htb_class structure,
and clamped to 32bits value during netlink dumps:

cl->xstats.tokens = clamp_t(s64, PSCHED_NS2TICKS(cl->tokens),
                            INT_MIN, INT_MAX);

Defining it as u32 is working since userspace (tc) is printing it as
signed int, but a correct definition from the beginning is probably
better.

In the same time, 'giants' structure member is unused since years, so
update the comment to mark it unused.
Signed-off-by: NFlorent Fourcot <florent.fourcot@wifirst.fr>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/uapi/linux/pkt_sched.h

@@ -395,9 +395,9 @@ enum {
 struct tc_htb_xstats {
 	__u32 lends;
 	__u32 borrows;
-	__u32 giants;	/* too big packets (rate will not be accurate) */
-	__u32 tokens;
-	__u32 ctokens;
+	__u32 giants;	/* unused since 'Make HTB scheduler work with TSO.' */
+	__s32 tokens;
+	__s32 ctokens;
 };
 
 /* HFSC section */