MINOR: log: use __send_log() with exact payload length

MINOR: log: use __send_log() with exact payload length

Historically, __send_log() was called with terminating NULL byte after
the message payload. But now that __send_log() supports being called
without terminating NULL byte (thanks to size hint), and that __sendlog()
actually stips any \n or NULL byte, we don't need to bother with that
anymore. So let's remove extra logic around __send_log() users where we
added 1 extra byte for the terminating NULL byte.

No change of behavior should be expected.