rib: remote prefix registration

resolve 3 bugs:

There are redundant registrations/unregistrations if loading the
config file multiple times.

Remote registration/unregistration will fail if localhop_security
is enabled.

Unstable RemoteRegistrator/UnregisterAdvanced test case.

Change-Id: I4437292e9f6c0e340c761ef7556a9bdc703ac06c
refs: #2294