| 1.113:
| be more cautious about tcp option length field.  drop bogus ones earlier.
| not sure if there is a real threat or not, but it seems that there's
| possibility for overrun/underrun (like non-NOP option with optlen > cnt).

it seems to me that this whole section of tcp_dooptions() should increment
a counter (e.g. "with bad options"). Agreement?

--jhawk