[network-control] Allow use of systemd-resolvd SetLinkDNS

snapd version: 2.54.3

This bug is a request to update the network-control interface to allow use of the system-resolved's SetLink* DBus methods. The network-manager interface slot allows use of these methods, so it makes sense that network-control should allow their usage too:

dbus (send)
     bus=system
     path="/org/freedesktop/resolve1"
     interface="org.freedesktop.resolve1.Manager"
     member="SetLink{DNS,MulticastDNS,Domains,LLMNR}"
     peer=(label=unconfined),

This is being requested as in a recent commercial case, we had to grant permission to use the network-manager slot as a workaround.