netdev-dpdk: Fix using uninitialized link_status.

netdev-dpdk: Fix using uninitialized link_status.

'rte_eth_link_get_nowait()' works only with physical ports.
In case of vhost-user port, 'link' will stay uninitialized and there
will be random messages in log about link status.

Ex.:
|dpdk(dpdk_watchdog2)|DBG|Port -1 Link Up - speed 10000 Mbps - full-duplex

Fix that by calling 'check_link_status()' only for physical ports.

Signed-off-by: Ilya Maximets <i.maximets@samsung.com>
Acked-by: Aaron Conole <aconole@redhat.com>
Acked-by: Daniele Di Proietto <diproiettod@vmware.com>