Function sendto

pub extern "C" fn sendto(
    fn_ptr: Option<&extern "C" fn(c_int, *const c_void, size_t, c_int, *const sockaddr, socklen_t) -> ssize_t>,
    fd: c_int,
    buf: *const c_void,
    len: size_t,
    flags: c_int,
    addr: *const sockaddr,
    addrlen: socklen_t,
) -> ssize_t