Controlling IPv6 MTU

[Roy Marples <roy%marples.name@localhost>]

Hi List

Currently, userland can only set the interface MTU SIOCSIFMTU.
IPv6 has it's own idea of what the MTU should be according to Router 
Adverts,
but there is no way of setting this outside of the RA itself.

I'm currently debugging dhcpcd with it's own RA implementation of 
handling
addresses and routes and this is one wall I'm hitting as my local setup
requires a lower MTU than 1500 and forcing a lower MTU for IPv4 isn't 
desirable.

Attached is a patch which adds SIOCSIFMTU_IN6 which I have not tested a 
lot
as I only just got home to a workable IPv6 network from a nice holiday 
but
I'd like eyes on it to spot anything wrong as I've never had to extend 
a kernel
struct or add a new ioctl before.

Thanks

Roy

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