Fix nameserver property for VLAN interfaces
Fix nameserver property for VLAN interfaces

Currently, nameservers of VLAN interfaces assigned by DHCP will not be
populated on DBus, and static nameservers previously set disappears on
DBus. This patch fixes this issue by loading nameserver info when
creating VLAN interface, same as how physical one does.

Tested:
Verified below 2 cases with VLAN interface
1. Nameservers assigned by DHCP is populated on DBus.
2. After restarting the xyz.openbmc_project.Network service, static
   nameservers previously configured is populated DBus.

Change-Id: I0da0c3c25b749de14994ed3f1647a21c1ecfac7d
Signed-off-by: Jiaqing Zhao <8cd80082a38ff4db4b284c7eb1282e9b764cf097@intel.com>

openbmc/phosphor-networkd,openbmc/phosphor-networkd