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

We may want to be able to run multiple listener process eventually, so the first step is to drop IMSG_CONTROLFD and keep the ctl stuff in the main process.

it's possibly a really useful tool to debug 9p servers, as it allows to manually craft messages, but it's just not there and I'd like to tag a 0.1 "soonish".

it's a bit easier to debug hexdumps now

twstat was serializing the qid in the wrong order. While here, add a comment before the qid definition too.

The idea behind woc_file is to create or open a file, but it's always used for writing fresh new content, so it's actually an error that it opens a file for writing without truncating it too. It means that if we write less content than what the file already has, we kepp garbage at the end. This adds an extra argument in send_fid (that is actually used only from woc_file now) so that we can pass KOTRUNC for do_open.

found by clang' static-analyzer