We'll grow the WS read buffer up to cdp-max-message-size (1MB default), but
never reclaim that space. A lot of drivers send large message upfront and then
settle into sending smaller ones.
This commit shrinks the buffer to 256KB (or cdp-max-message-size, whichever is
smaller) after 8 consecutive small message (tracking consecutive messages to
prevent a spat of allocation -> shink -> allocation -> shrink ->...)
23ab2df58e