Always push the DNS server to resolved even if the mode is not systemd-resolved

Hi,

resolved can be used 2 two mode, either using the stub resolver or by using nss-resolved (the later seems recommended)

At the moment the DNS servers are only pushed to resolved if the mode is systemd-resolved, NM only detects if resolved is used by looking whether /etc/resolv.conf is a symlink, that means that for people using nss-systemd the DNS are not set and if the user is connecting to a VPN, resolved could take the wrong DNS server (aka the one outside of the VPN) and things might break or leak

To avoid that, shouldn't the DNS always be pushed to resolved (if it's running) even if the mode is not systemd-resolved?