[NET]: Fix HH_DATA_OFF.

When the hardware header size is a multiple of HH_DATA_MOD, HH_DATA_OFF()
incorrectly returns HH_DATA_MOD (instead of 0). This affects ieee80211 layer
as 802.11 header is 32 bytes long.
Signed-off-by: NJiri Benc <jbenc@suse.cz>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

include/linux/netdevice.h

@@ -204,7 +204,7 @@ struct hh_cache
 	/* cached hardware header; allow for machine alignment needs.        */
 #define HH_DATA_MOD	16
 #define HH_DATA_OFF(__len) \
-	(HH_DATA_MOD - ((__len) & (HH_DATA_MOD - 1)))
+	(HH_DATA_MOD - (((__len - 1) & (HH_DATA_MOD - 1)) + 1))
 #define HH_DATA_ALIGN(__len) \
 	(((__len)+(HH_DATA_MOD-1))&~(HH_DATA_MOD - 1))
 	unsigned long	hh_data[HH_DATA_ALIGN(LL_MAX_HEADER) / sizeof(long)];