TCP receive windows broken in 4.14.48

Hi,

4.14.48 can cause abnormally small TCP receive windows when the sender is faster than the receiver; see https://github.com/coreos/bugs/issues/2457 for details. Reverting "tcp: avoid integer overflows in tcp_rcv_space_adjust()" fixes it. Backporting 02db55718d53 ("tcp: do not overshoot window_clamp in tcp_rcv_space_adjust()"), which is its parent commit upstream, also fixes it.

--Benjamin Gilbert