The previous definition of TCB_NAME_LENGTH assumed that the TCB was
split evenly into the cnode region and the rest. It did this by
calculating the size of the rest by using the size of the cnode
region. In actual fact the cnode region might be smaller, making
the size of the rest the size of the total tcb block size, minus
the cnode size. The max name length is therefore this region, minus
the size of the tcb_t
