Use loopback interest to serve own certificate
Nlsr serves certificate to others from its own certificate store. To get certificate from others, Nlsr depends on DirectFetcher.
But when it needs its own certificate to verify data/ interest (e.g. command interest sent from its own operator), it can't fetch it. We bypass the problem by putting the certificates in DirectFetcher's TrustAnchorContainer.
This problem can be solved by using loopback interest. When Nlsr sets interest filter for its own certificate, we allow loopback interest. So when Nlsr asks for its own authoritative certificates, it can serve them from the certificate store.