vlan_interface: Write configs from parser
vlan_interface: Write configs from parser

This guarantees the values are valid and that the file is always swapped
out atomically instead of written piecewise

Tested: Manually created and modified a VLAN device and saw that the
config options were persisted to the RWFS

Change-Id: Ia3d61110ba54ec6b7ed5be61192c90fbaaf20764
Signed-off-by: William A. Kennington III <30fff5198f4d10ca1117e5f3ec82f3b4b8900d81@google.com>

openbmc/phosphor-networkd,openbmc/phosphor-networkd