hack MSS of packets outgoing via interface with small MTU, to workaround
path MTU discovery problems.
Written by Alexey Popov, with some cleanups from me. There are also plans
to improve mpd port, so that it uses this node, instead of doing MSS
hacking in userland, when 'enable tcpmssfix' option is on.
Submitted by: Alexey Popov <lollypop@flexuser.ru>
