Move network code to libtor-net.

There are some additional changes to come: those points are marked
by XXXX.

src/rust/build.rs

@@ -151,6 +151,7 @@ pub fn main() {
             // moving forward!
             cfg.component("tor-crypt-ops-testing");
             cfg.component("or-testing");
+            cfg.component("tor-net");
             cfg.component("tor-log");
             cfg.component("tor-lock");
             cfg.component("tor-fdio");