networkctl: extend "networkctl status" per-interface output to include LLDP info

networkctl: extend "networkctl status" per-interface output to include LLDP info

This adds a small and useful field to the "systemctl status" output: the
router(s) the interface is connected to as reported via LLDP. Example output:

● 2: enp0s25
       Link File: /usr/lib/systemd/network/99-default.link
            Type: ether
           State: degraded (configured)
            Path: pci-0000:00:19.0
          Driver: e1000e
    Connected To: GS1900 on port 2 (foobar)

i.e. the last line is the relevant one.