Pass an Interactor to new_connection().

Thanks to the previous commit, this new parameter can replace two of
the existing ones: instead of passing a LogPolicy and a Seat, we now
pass just an Interactor, from which any proxy implementation can
extract the LogPolicy and the Seat anyway if they need it.

proxy/nosshproxy.c

@@ -10,8 +10,7 @@ const bool ssh_proxy_supported = false;
 Socket *sshproxy_new_connection(SockAddr *addr, const char *hostname,
                                 int port, bool privport,
                                 bool oobinline, bool nodelay, bool keepalive,
-                                Plug *plug, Conf *conf,
-                                LogPolicy *clientlp, Seat **clientseat)
+                                Plug *plug, Conf *conf, Interactor *itr)
 {
     return NULL;
 }