Good for debugging (you have to send SIGUSR1 to lightning_gossipd to turn
it on though, and --log-level=io on the lightningd cmdline to have it
output IO messages by default).
I also noticed that io_tor_connect_after_req_host() does a useless
test on reach->buffer[0] after it's *written*: remove it.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>