Changes

server: Store read buf max len as conn field

This will be useful later on when adding pcapng support, since checks
will become more complex due to different data types to be checked,
based on information from pcap vs pcapng gathered from magic field
inside the received link_hdr buffer.

Change-Id: I8f62aa0bdb04e73223c0c6803a58241f83a5ebe9