igb: Do not parse past IP header on fragments beyond the first

This change makes it so that only the first fragment in a series of fragments
will have the L4 header pulled.  Previously we were always pulling the L4
header as well and in the case of UDP this can harm performance since only the
first fragment will have the header, the rest just contain data which should
be left in the paged portion of the packet.

Signed-off-by: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>

drivers/net/ethernet/intel/igb/igb_main.c

@@ -6145,20 +6145,23 @@ static unsigned int igb_get_headlen(unsigned char *data,
 		if (hlen < sizeof(struct iphdr))
 			return hdr.network - data;
 
-		/* record next protocol */
-		nexthdr = hdr.ipv4->protocol;
-		hdr.network += hlen;
+		/* record next protocol if header is present */
+		if (!hdr.ipv4->frag_off)
+			nexthdr = hdr.ipv4->protocol;
 	} else if (protocol == __constant_htons(ETH_P_IPV6)) {
 		if ((hdr.network - data) > (max_len - sizeof(struct ipv6hdr)))
 			return max_len;
 
 		/* record next protocol */
 		nexthdr = hdr.ipv6->nexthdr;
-		hdr.network += sizeof(struct ipv6hdr);
+		hlen = sizeof(struct ipv6hdr);
 	} else {
 		return hdr.network - data;
 	}
 
+	/* relocate pointer to start of L4 header */
+	hdr.network += hlen;
+
 	/* finally sort out TCP */
 	if (nexthdr == IPPROTO_TCP) {
 		if ((hdr.network - data) > (max_len - sizeof(struct tcphdr)))