1/ increase the tun MTU from 1500 to 1600 to allow it to be used with
packets formatted according to RFC1490 and RFC1717
2/ allow the tsleep() when reading, to be interruptable by signals
so that one can now do:
od -xc </dev/tun0
to dump packets for debugging without getting hung.
Passed on by: Archie@whistle.com (archie Cobbs)
Nice but not neccessary in 2.2