ip: introduce ip_is_fragment helper inline function

There are enough instances of this:

    iph->frag_off & htons(IP_MF | IP_OFFSET)

that a helper function is probably warranted.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/drivers/net/ioc3-eth.c b/drivers/net/ioc3-eth.c
index 32f07f8..318a25a 100644
--- a/drivers/net/ioc3-eth.c
+++ b/drivers/net/ioc3-eth.c
@@ -532,7 +532,7 @@
 		return;
 
 	ih = (struct iphdr *) ((char *)eh + ETH_HLEN);
-	if (ih->frag_off & htons(IP_MF | IP_OFFSET))
+	if (ip_is_fragment(ih))
 		return;
 
 	proto = ih->protocol;