[AGENT] add network metrics

[StrayLittlePunk]

This PR is for:

• Agent

Fixes

• client latency 1. The first waiting time: the time from the client's first request to the completion of the three-way handshake (the client sends SYN-ACK-ACK) or the time from the client's first request to the time from receiving the server data 2. subsequent waiting time: The time between the client request and the last server response (Payload > 1)
• Transport layer throughput: number of SYN packets number of SYN-ACK packets number of Retran SYN packets number of Retran SYN-ACK packets

[sharang]

需要增加 SYN重传、SYNACK重传 两个指标