gro: support UDP/IPv4

gro: support UDP/IPv4

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
UDP fragments immediate after they are received from
a physical NIC. It is very helpful in OVS DPDK VLAN use
case.

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