netperf: enable multiqueue in guest by ethtool

  ethtool -L $ethname combined $N

Signed-off-by: Amos Kong <akong@redhat.com>
netperf: fix wrong IP in netperf cmdline

commit 63ada005 introduced a regression, it wrongly update the server_ip
to ip address of control connection.

We have two nics, the first (virtio-net) is data connection, the second
nic (non virtio-net) is control connection.

Signed-off-by: Amos Kong <akong@redhat.com>