backport: "Add support for setting phys-dev for VXLAN interfaces."

backport: "Add support for setting phys-dev for VXLAN interfaces."

backporting the following commit to master-next:

commit eb92e5efff776602081b8bbd2cc74462293c4b79
Author: Maximilian Wilhelm <max@rfc2324.org>
Date:   Thu Oct 6 19:22:06 2016 +0200

    Add support for setting phys-dev for VXLAN interfaces.

      Add interface configuration option »vxlan-physdev« to set »dev« attribute
            of VXLAN interfaces and a check for the running configuration.

    Signed-off-by: Maximilian Wilhelm <max@rfc2324.org>
This backport also:
 - adds support for ifquery --running
 - uses the netlink cache
 - includes some pep8 fixes

Signed-off-by: Julien Fortin <julien@cumulusnetworks.com>
Signed-off-by: Maximilian Wilhelm <max@rfc2324.org>
Co-authored-by: Julien Fortin <julien@cumulusnetworks.com>
Co-authored-by: Maximilian Wilhelm <max@rfc2324.org>