body server control: allowlegacyconnects

Which IPs or subnets to allow connections from, even though they are not
using the latest protocol.
Stylistic changes.
Fix old protocol client_code segfault.

Also reverted opaqueness of ConnectionInfo and restored direct access to
it for the relevant client_code. I expect that at least for libcfnet
internal usage I don't have to deal with abstraction layers.
Silence warning when compiling without XML.
Moving documentation in .c files from header files.

This is documentation the programmer has to see the moment he looks up
the function name, and currently most (all?) editors take you to the
implementation, not the declaration.
Demoted cf-serverd client-triggered errors from LOG_LEVEL_ERR to NOTICE.
body common control: protocol_version
Define CF_PROTOCOL_LATEST same as CF_PROTOCOL_TLS.

Also make the code a bit more future-proof, if more than one protocols
ever exist inside the TLS layer.