Function hyper_clientconn_options_http2 

#[unsafe(no_mangle)]
pub extern "C" fn hyper_clientconn_options_http2(
    opts: *mut hyper_clientconn_options,
    enabled: c_int,
) -> hyper_code

Available on crate feature ffi and hyper_unstable_ffi only.

Set whether to use HTTP2.

Pass 0 to disable, 1 to enable.