net/virtio: add missing supported features

net/virtio: add missing supported features

The virtio features VIRTIO_NET_F_CSUM, VIRTIO_NET_F_HOST_TSO4
and VIRTIO_NET_F_HOST_TSO6 are supported by the virtio PMD.
But they are missing in the supported feature set. And since
below commit:

commit 4174a7b59d05 ("net/virtio: improve Tx offload features negotiation")

Virtio PMD will announce the Tx offloading capabilities based
on the features read from the device. And virtio-user won't
report the features which are not in virtio-PMD's supported
feature set. So since that commit, virtio-user won't announce
the DEV_TX_OFFLOAD_UDP_CKSUM, DEV_TX_OFFLOAD_TCP_CKSUM and
DEV_TX_OFFLOAD_TCP_TSO offloading capabilities even if the
vhost backend supports them.

This patch adds these missing features, and virtio-user will
report them if the backend supports them.

Fixes: 142678d42959 ("net/virtio-user: fix wrongly get/set features")
Cc: stable@dpdk.org
Signed-off-by: Tiwei Bie <tiwei.bie@intel.com>
Reviewed-by: Maxime Coquelin <maxime.coquelin@redhat.com>