- Switch from the old 'log' class (ERR/DBG/etc) to a better
'logger' class. Also use LOG_* as defined in syslog.h.
- Make it possible to read debug messages even for release.
- Add a new argument (-v|--verbose) to 'ndppd' to change
verbosity level.
* Make iface::read() return a bit more generic address (sockaddr).
* Add is_unicast() and is_multicast() to address.
* Set default config path to "/etc/ndppd.conf".
* Silently ignore solicit messages with bad saddr and/or daddr.