Extend ifaddr_event to pass ifaddr and event type to handler

[ae]

Summary

ifaddr_event is used to notify registered consumer about changes for AF_INET/AF_INET6 addresses.
But handler is forced to track all needed addresses and for every notify look what address is deleted or added.
This patch introduces new ifaddr_event_ext event. Now consumer can register handler for this event, and the handler will receive the type of event IFADDR_EVENT_ADD or IFADDR_EVENT_DEL, and also pointer to ifaddr.
The patch also implements ifaddr_event in the ifaddr_event_ext handler.

[eugen_grosbein.net]

This also needs an update for share/man/man9/EVENTHANDLER.9