Function us_dispatch_open 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn us_dispatch_open(
    s: *mut c_void,
    is_client: i32,
    ip: *mut u8,
    ip_length: i32,
) -> *mut c_void

Socket opened (accept or connect completion). Routes to group.vtable.on_open if available, else returns s.