virtio: add default Tx configuration
virtio: add default Tx configuration

When I tried to launch test-pmd on KVM guest of Fedora21, I got following error:

Configuring Port 0 (socket 0)
Fail to configure port 0 tx queues
EAL: Error - exiting with code: 1
  Cause: Start ports failed

I found that the error caused here, and actual error message was
"TX checksum offload not supported".

This patch adds default_txconf on virtio pmd, to avoid the error.

Signed-off-by: Takuya Asada <4ebfb6f510af412d6e89fefa3ab96d9c8b5e3fff@cloudius-systems.com>
Acked-by: Pablo de Lara <28355d9cfe41bb8148aea0fb24f47aae8f4217a1@intel.com>

john-mcnamara-intel/dpdk,msune/dpdk,msune/dpdk,msune/dpdk,msune/dpdk,mixja/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork,tsphillips/dpdk-fork,venkynv/dpdk-mirror,mixja/dpdk,tsphillips/dpdk-fork,mixja/dpdk,venkynv/dpdk-mirror,venkynv/dpdk-mirror,mixja/dpdk,venkynv/dpdk-mirror,john-mcnamara-intel/dpdk,tsphillips/dpdk-fork