SDN-IP main class, responsible for the following functions:
1. Start a BGPSpeaker as an iBGP Speaker on Ryu, and connect with other BGPSpeakers in the SDN domain to obtain route information (SDN-IP BGPSpeaker<---->Internal BGPSpeaker);
Corresponding method: __init__()
2. Establish a connection between BGPSpeaker in the SDN domain and BGPSpeaker outside the domain (Internal BGPSpeaker<--->External BGPSpeaker);
Corresponding method: bgp_packet_in_handler()
3. Establish a data path to access external hosts (Traffic--->External Hosts)
Corresponding method: best_path_change_handler()
5. Establish a path for external hosts to access the local host (External Host---> Local Host)