swcore[new mpm]: page allocator (both old and new) modified to enable a new way of page usecnt handling: we store the usecnt only in the first page of the pck, the non-first pages have usecnt=1. When pck is sent on the output port, only the usecnt of the first page is decremented unless the usecnt==1, then we free all the pages allocated to the pck, so the page allocator needs to indicate if the usecnt is 1