Add metadata fields for messages from socket_server input

[XU-Nuo]

I have many tcp clients connect to the same socket on the machine runs the redpanda connect, and many operations I want to perform is client-based, such as:

• sending back heartbeat messages
• grouping
• deduplication
• redirecting

It would be useful to fill the metadata fields of the messages received by socket_server, using the information from different network layer, for example, source IPs from the IP layer and ports from transport layer. Other inofrmation can be useful to others but not for my use case, such as the source MAC address from the data link layer.