[NETWORK-OKR] Bidirectional connection and nat transveral

[pieceofr]

Current bitmark node requires public IP to connect with other nodes. This limits the utilization rate of bitmark nodes. The bi-directional connection enables that two nodes require only one public IP to connect with each other. Further more, nat transversal can enhance the requirement of using public ip. The task is to research on existing golang libraries for bidirectional and nat transversal.

• Research on bidirectional tcp
• Research on Nat transversal issue (20%)
• Research on golang library
• Testing on the libraries in bidirectional tcp
• Testing on nat transversal feature
• Create a simple P2P module to illustrate the bidirectional connection works