net: Add GRO support for vxlan traffic

Add GRO handlers for vxlann, by using the UDP GRO infrastructure.

For single TCP session that goes through vxlan tunneling I got nice
improvement from 6.8Gbs to 11.5Gbs

--> UDP/VXLAN GRO disabled
$ netperf  -H 192.168.52.147 -c -C

$ netperf -t TCP_STREAM -H 192.168.52.147 -c -C
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.52.147 () port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB

 87380  65536  65536    10.00      6799.75   12.54    24.79    0.604   1.195

--> UDP/VXLAN GRO enabled

$ netperf -t TCP_STREAM -H 192.168.52.147 -c -C
MIGRATED TCP STREAM TEST from 0.0.0.0 (0.0.0.0) port 0 AF_INET to 192.168.52.147 () port 0 AF_INET
Recv   Send    Send                          Utilization       Service Demand
Socket Socket  Message  Elapsed              Send     Recv     Send    Recv
Size   Size    Size     Time     Throughput  local    remote   local   remote
bytes  bytes   bytes    secs.    10^6bits/s  % S      % S      us/KB   us/KB

 87380  65536  65536    10.00      11562.72   24.90    20.34    0.706   0.577

Signed-off-by: Shlomo Pongratz <shlomop@mellanox.com>
Signed-off-by: Or Gerlitz <ogerlitz@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/include/net/vxlan.h b/include/net/vxlan.h
index 6b6d180..5deef1a 100644
--- a/include/net/vxlan.h
+++ b/include/net/vxlan.h
@@ -21,6 +21,7 @@
 	struct rcu_head	  rcu;
 	struct hlist_head vni_list[VNI_HASH_SIZE];
 	atomic_t	  refcnt;
+	struct udp_offload udp_offloads;
 };
 
 struct vxlan_sock *vxlan_sock_add(struct net *net, __be16 port,