Checksum offload is implemented in VXLAN encap over both IPv4 and
IPv6. It is enabled, however, only for VXLAN over IPv6 because UDP
checksum is needed only for IPv6 and optional for IPv4.
Change-Id: Ib879f4f6da7346ba5e079d321c1dfd630f5058b8 Signed-off-by: John Lo <loj@cisco.com>