drop unused function listen_by_id

kill unused variable

tweak debug call

drop unnecessary debugging log

add IMSG_CTL_DEBUG to debug the opened fid meant to be used from kamictl to dump all the opened fid by every connection.

listener: enable config reload

cache listener flags in struct client this saves us from the small chance that a client accepted before reconf uses the flags from a listener post reconf.

fix restart in listener drop connections in the handshake phase: the listener from where they've been accepted is now being replaced and its id is no more meaningful. Clients for which we have already sent an auth request are kept.

drop unused flag done for clients

remove clients from the splay at the start of close_conn

use serial ids and drop usage of arc4random it's not so useful here and not (directly) used anywhere else.

listener: correctly swap config after reload and don't forget to free the current config!

use STAILQ_INIT instead of memcpy(head, 0) to init the queues

call clear_config from parse.y in listener_shutdown

listener: handle IMSG_CTL_LOG_VERBOSE adjust the logging level and forward it to every client process so they can do so too.