MPPE_OVHD
if (osize < isize + MPPE_OVHD + 2) {
osize, osize + MPPE_OVHD + 2);
osize = isize + MPPE_OVHD + 2;
obuf += MPPE_OVHD;
if (isize <= PPP_HDRLEN + MPPE_OVHD) {
if (osize < isize - MPPE_OVHD - 1) {
osize, isize - MPPE_OVHD - 1);
osize = isize - MPPE_OVHD - 2; /* assume no PFC */
ibuf += PPP_HDRLEN + MPPE_OVHD;
isize -= PPP_HDRLEN + MPPE_OVHD; /* -6 */