net: sock: do not set sk_cookie in sk_clone_lock()

The only call site of sk_clone_lock is in inet_csk_clone_lock,
and sk_cookie will be set there.
So we don't need to set sk_cookie in sk_clone_lock().

Reviewed-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: Yafang Shao <laoar.shao@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>