setting the other end's TCP segment size

[perryh at pluto.rain.com]

> 1) create a static ARP entry, this will create an entry to
>   the routing table i.e. arp -S IPADDR MACADDR
> 2) modify the mtu for that destination
>   i.e. route change IPADDR -mtu MTU

Seems to work fine :)

One problem with this approach is that a hard-coded MAC address
would break if the destination's MAC address changed :( but this
can be scripted around by pinging the destination (to ensure that
it's up, and get an arp entry "the usual way"), then reading the
MAC address from the arp table.

d=192.168.200.3
ping -c 1 $d && \
arp -S $d ` arp -n $d | sed -e 's/^.* at //' -e 's/ on .*$//' ` && \
route change $d -mtu 640