Replace netsh for handling MTU

[dlon]

Also, use the simpler GetIpInterfaceEntry for obtaining the interface MTU. This should reliably work.

[dlon]

Fixed the clippy warnings here: #18

[dlon]

Looks like the version needs to be bumped. Do you want me to do that?

[ssrlive]

Needn't, since 'stdcall' is 'system` in windows. I have no time to review it right now, maybe tomarrow.

[dlon]

Do you think you could have a look at this?

[ssrlive]

I apologize for the long delay, as I encountered numerous setbacks with setting the MTU in Wintun. This is due to a flaw in the Wintun kernel driver. The MTU settings weren't actually working, but many disagreed with me. To quell the debate, I agreed with these opinions and pretended that the MTU modifications were effective.

On the other hand, I don't trust the various dazzling APIs provided by Microsoft for setting network parameters, as I've suffered countless losses using them. Therefore, I prefer to use Microsoft's command-line tools like net to set parameters; at least they are thoroughly tested and effective.

Did your modifications to these MTU settings actually work? If you have thoroughly verified them, they do indeed work and have been proven in practice. I would be happy to merge this PR.

[dlon]

No worries. I've done some tests below.

The MTU is correct according to this: netsh interface ipv4 show interface

Also, running the udp-echo example (sudo cargo r --example udp-echo) with different MTUs works as expected. If I ping the address with the DF flag set and set the size to anything above MTU - header sizes, it fails as expected:

>ping 10.28.13.100 -l 1373 -f

Pinging 10.28.13.100 with 1373 bytes of data:
Packet needs to be fragmented but DF set.

I could also add that the Mullvad VPN app has been using SetIpInterfaceEntry/GetIpInterfaceEntry for many years. :)