datapath/actions: Mark recalculate_csum as likely in set_ipv6_addr().

The ‘recalculate_csum’ is almost always ‘true’.  It is false only if
the ipv6 nexthdr is an extension header, and a routing header is
found.  For the majority of ipv6 packets this would not be the case,
so this can be marked as 'likely'.

Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Jesse Gross <jesse@nicira.com>

datapath/actions.c

@@ -394,7 +394,7 @@ static void set_ipv6_addr(struct sk_buff *skb, u8 l4_proto,
 			  __be32 addr[4], const __be32 new_addr[4],
 			  bool recalculate_csum)
 {
-	if (recalculate_csum)
+	if (likely(recalculate_csum))
 		update_ipv6_checksum(skb, l4_proto, addr, new_addr);
 
 	skb_clear_hash(skb);