use struct channel_open_info.
* src/proxy_x11forward.c (do_proxy_open_x11): Likewise.
* src/proxy_tcpforward.c (do_proxy_open_direct_tcpip): Likewise.
* src/proxy_session.c (do_proxy_open_session): Likewise.

Rev: src/proxy_agentforward.c:1.3
Rev: src/proxy_session.c:1.7
Rev: src/proxy_tcpforward.c:1.4
Rev: src/proxy_x11forward.c:1.3