PRN_BIDI
if (cap & PRN_BIDI) {
cap &= ~PRN_BIDI;
if (cap & PRN_BIDI) {
cap &= ~PRN_BIDI;
if ((ifcap ^ new_ifcap) & ~PRN_BIDI) {
if (new_ifcap & PRN_BIDI) { /* go bidirectional */
ifcap |= PRN_BIDI;