NDR_PDU_BLOCK_SIZE
size = (pdu_size_hint == 0) ? NDR_PDU_BLOCK_SIZE : pdu_size_hint;
#define NDR_PDU_BLOCK_MASK (NDR_PDU_BLOCK_SIZE - 1)
(((N) + NDR_PDU_BLOCK_SIZE) & ~NDR_PDU_BLOCK_MASK)