ModemManager: disable modem functionality for now

org.freedesktop.ModemManager changed to ModemManager1 as well as
its API.
To be implemented later.
Merge pull request #140 from pwieczorkiewicz/modemsoff

ModemManager: disable modem functionality for now
Merge pull request #142 from mtomaschewski/dhcp-leases

addrconf: initial lease writting/parsing helpers