[NAN] Removed NAN event registration - dispatch all callbacks.

All events dispatched by default - there's no reason to ignore events.
The specific identity changed events for which there are use-cases to
get or ignore is controlled through a new configuration.

(cherry-pick of a5ed6937)

Bug: 27607613
Change-Id: I289a36157b55270c58311a016ef79f8746e0e0a0
(cherry picked from commit 574b3fb8)