gro: support VXLAN UDP/IPv4

gro: support VXLAN UDP/IPv4

VXLAN UDP/IPv4 GRO can help improve VM-to-VM UDP
performance when UFO or GSO is enabled in VM, GRO
must be supported if UFO or GSO is enabled,
otherwise, performance can't get big improvement
if only GSO is there.

With this enabled in DPDK, OVS DPDK can leverage it
to improve VM-to-VM UDP performance, it will reassemble
VXLAN UDP/IPv4 fragments immediate after they are
received from a physical NIC. It is very helpful in
OVS DPDK VXLAN use case.

Signed-off-by: Yi Yang <yangyi01@inspur.com>
Acked-by: Jiayu Hu <jiayu.hu@intel.com>