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/myri10ge/myri10ge.c b/drivers/net/myri10ge/myri10ge.c
index 3e89a84..3ed5f35 100644
--- a/drivers/net/myri10ge/myri10ge.c
+++ b/drivers/net/myri10ge/myri10ge.c
@@ -2257,7 +2257,7 @@
 	*ip_hdr = iph;
 	if (iph->protocol != IPPROTO_TCP)
 		return -1;
-	if (iph->frag_off & htons(IP_MF | IP_OFFSET))
+	if (ip_is_fragment(iph))
 		return -1;
 	*hdr_flags |= LRO_TCP;
 	*tcpudp_hdr = (u8 *) (*ip_hdr) + (iph->ihl << 2);