D-Bus: Add ConfigFile parameter into the interface properties

D-Bus: Add ConfigFile parameter into the interface properties

This patch aims to expose the configuration file path as an interface
property, like is done with the driver and the bridge name. Doing so,
higher layer programs become responsible to recreate interfaces with the
correct configuration file path when programs need to remove them.

Signed-off-by: Jose Blanquicet <blanquicet@gmail.com>