NLSR

When nlsrc advertise and nlsrc withdraw commands is invoked when NFD is ready but NLSR is not yet started, these commands would receive Nack from NFD.
Currently, these commands would print "Request timed out (code: 10060, error: Nack)" and then exit with zero.
This makes it difficult to retry the advertise/withdraw operation in a bash script.

These commands should return a non-zero exit code if it cannot reach NLSR or if it receives errors such as authentication rejection.
However, in case of advertising/withdrawing an already advertised/withdrawn prefix, the command should still return zero exit code because the desired effect is already in place.