[NET]: Convert hh_lock to seqlock.

The hard header cache is in the main output path, so using
seqlock instead of reader/writer lock should reduce overhead.

Signed-off-by: Stephen Hemminger <shemminger@osdl.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/linux/netdevice.h b/include/linux/netdevice.h
index c57088f..631cec4 100644
--- a/include/linux/netdevice.h
+++ b/include/linux/netdevice.h
@@ -199,7 +199,7 @@
                                          */
 	u16		hh_len;		/* length of header */
 	int		(*hh_output)(struct sk_buff *skb);
-	rwlock_t	hh_lock;
+	seqlock_t	hh_lock;
 
 	/* cached hardware header; allow for machine alignment needs.        */
 #define HH_DATA_MOD	16