netdev-dpdk: Consistent variable naming.

netdev-dpdk: Consistent variable naming.

In different functions we use different variable names ('netdev_', 'netdev',
'dev', 'vhost_dev', ...) for the same objects.

This commit changes the code to comply with the following convention:

'struct netdev':'netdev'
'struct netdev_dpdk':'dev'
'struct virtio_net':'virtio_dev'
'struct netdev_rxq':'rxq'
'struct netdev_rxq_dpdk':'rx'

Also, 'dev->up.' is replaced by 'netdev->', where 'netdev' was already
defined.

Suggested-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Tested-by: Ilya Maximets <i.maximets@samsung.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Acked-by: Mark Kavanagh <mark.b.kavanagh@intel.com>