The merge commit 0fd89a1a
of commit b6ec1e8b
was slightly incomplete.

ReadView::mem_valid(): Use the correct primitive
MEM_MAKE_ADDRESSABLE(), because MEM_UNDEFINED() now has
no effect on ASAN.

recv_sys_t::alloc(), recv_sys_t::add(): Use MEM_MAKE_ADDRESSABLE()
instead of MEM_UNDEFINED(), to get the correct behaviour for ASAN.
For Valgrind and MSAN, there is no change in behaviour.

recv_sys_t::free(), recv_sys_t::clear(): Before freeing memory to
buf_pool.free_list, invoke MEM_MAKE_ADDRESSABLE() on the entire
buf_block_t::frame, to cancel the effect of MEM_NOACCESS() in
recv_sys_t::alloc().