if -b was given without a explicit host, it defaulted to listen on any address. it's not a good idea given this would allow anyone on the same network to (ab)use the ssh forwarding.

* fix handling of HAVE_LIBEVENT2 * provide shims for pledge/unveil

socket splicing allows to do zero-copy data transfers between sockets. This adds a specific implementation for OpenBSD using the setsockopt SO_SPLICE and a default implementation with libevent (that is the old code doing the copy in userland.) It's possible to do the same on linux with splice(2), not implementd though.

this way we can run the auto-configuration after the args handling and provide a better output.