IP dynamic address hack-port v0.03

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This stuff allows diald ONESHOT connections to get established by dynamically changing packet source address (and socket's if local procs). It is implemented for TCP diald-box connections(1) and IP_MASQuerading(2).

If enabled[*] and forwarding interface has changed:

1) Socket (and packet) source address is rewritten ON RETRANSMISSIONS while in SYN_SENT state (diald-box processes).

2) Out-bounded MASQueraded source address changes ON OUTPUT (when internal host does retransmission) until a packet from outside is received by the tunnel.

This is specially helpful for auto dialup links (diald), where the ``actual'' outgoing address is unknown at the moment the link is going up. So, the *same* (local AND masqueraded) connections requests that bring the link up will be able to get established.

[*] At boot, by default no address rewriting is attempted. 
  To enable:
     # echo 1 > /proc/sys/net/ipv4/ip_dynaddr
  To enable verbose mode:
     # echo 2 > /proc/sys/net/ipv4/ip_dynaddr
  To disable (default)
     # echo 0 > /proc/sys/net/ipv4/ip_dynaddr

Enjoy!

-- Juanjo