(#1) Log when the interface address changes
(#1) Implement separate IPv4 and IPv6 announcement timers

* IPv4 announcements go to 224.0.0.1:5350, IPv6 announcements go to
  [ff02::1]:5350 as per the RFC's.
* IPv6 address changes only trigger announcements from IPv6 listening
  addresses, separate from IPv4 address changes, etc.
* (FIXME) Currently IPv6 announcements send the IPv4 NAT-PMP packet.