Clean-up basic Command Line Interface

The first step of the gosdn code used the spf13 package to implement a basic command line interface used when starting the gosdn program.

However, go built-in flags are the better way to go forward, as this will result in a reduced number of dependencies.

Do this:

• Add flags support for current cli options
• Remove spf3
• Add additional flags and their defaults, such as grpc-CLI listener address and port etc