dpdk: resurrect removed code [VPP-1245]

dpdk: resurrect removed code [VPP-1245]

https://gerrit.fd.io/r/#/c/7701/ accidentally removed 3 lines of code in
dpdk/device/init.c which were added by https://gerrit.fd.io/r/#/c/7826/

case VNET_DPDK_PMD_VHOST_ETHER:
xd->port_type = VNET_DPDK_PORT_TYPE_VHOST_ETHER;
break;

Those lines were needed to recognize vhost-user interface which is created
via vdev command in dpdk and display VhostEthernet. Without them,
UnknownEthernet is displayed.

Change-Id: I6d7ee6aecc6a415fbb7308595d515649475bcd5f
Signed-off-by: Steven <sluong@cisco.com>