[Dnssec-trigger] [Bug] incorrect DNS servers are used when network-manager connects to VPN

[Ralf Jung]

Dear dnssec-trigger developers,

I hope this is the right channel for a bugreport, please excuse me if it
is not.
First of all, thanks a lot for making this awesome program. It is
exactly what I looked for to finally use DNSSEC on my Laptop :)

I am having a problem though when using dnssec-trigger with
network-mananger and VPN connections. After the connection is
established, dnssec-trigger still uses the DNS servers supplied by the
physical "outer" connection, instead of the ones that came from the VPN.
Thus, DNS does not work if the servers are configured to serve the local
network only.
I can see the following in the system journal after the VPN connection
is established:

> Sep 01 11:12:12 r-schnelltop logger[3766]: dnssec-trigger-hook(networkmanager) vpn0 vpn-up added global DNS 134.96.7.100 134.96.7.99 134.96.7.5

However, these are the DNS servers of wlan0. The VPN returned a
different set of DNS servers.
Only after supplying the VPN-DNS-servers to dnssec-trigger-control,
everything works as expected.

I am using the packages in Debian testing, and also reported this issue
downstream: <https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=760147>
The version of NM is 0.9.10.0, dnssec-trigger is at version 0.13~svn685.

Kind regards
Ralf