ldpd: use synchronous channels for sending log messages

ldpd: use synchronous channels for sending log messages

This is necessary to guarantee that all log messages sent from the child
processes are received in the parent process right away.

Without this patch, when a child process calls fatal() or fatalx(),
the log messages don't make it to the parent because the child doesn't
have a chance to flush its buffers before exiting.

Signed-off-by: Renato Westphal <renato@opensourcerouting.org>