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/bonding/bond_main.c b/drivers/net/bonding/bond_main.c
index d117280..ebb1d21 100644
--- a/drivers/net/bonding/bond_main.c
+++ b/drivers/net/bonding/bond_main.c
@@ -3438,7 +3438,7 @@
 	int layer4_xor = 0;
 
 	if (skb->protocol == htons(ETH_P_IP)) {
-		if (!(iph->frag_off & htons(IP_MF|IP_OFFSET)) &&
+		if (!ip_is_fragment(iph) &&
 		    (iph->protocol == IPPROTO_TCP ||
 		     iph->protocol == IPPROTO_UDP)) {
 			layer4_xor = ntohs((*layer4hdr ^ *(layer4hdr + 1)));