Setting the MTU for an automatically configured "eth" network interface?

[Gilles Gravier]

Hi!

So my Feisty 7.04 machine gets its network address directly and 
automatically via DHCP... using the default network configuration wizard.

Problem is that I want to set the MTU to something different than 1500. 
I didn't find an option in the wizard to change the MTU for eth0. Where 
can I do that?

Thanks in advance,
Gilles.
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