Fix test using com.docker.network.mtu

[thaJeztah]

This should be com.docker.network.driver.mtu

fixes #1906

ping @abhinandanpb PTAL

[abhi]

LGTM

[fcrisciani]

@thaJeztah should we investigate why the test is passing?

[thaJeztah]

Yes, if you have thoughts, definitely 👍

[abhi]

since its an option I dont there is a check to verify.

[fcrisciani]

don't have much context in this area, but I guess if the option is for a driver would have to contain the .driver. string I imagine, in that case I would say that we do not validate at the level of libnetwork, but if that string is not there, will probably mean that is a libnetwork option, so we can actually validate it and return an error if not recognized. What do you guys think? @thaJeztah @abhinandanpb

[abhi]

I think for this test if we want to check if mtu is set appropriately which would also mean we would have validated the option - we can add a check network.mtu == 1600 and network is returned by controller.NewNetwork

[fcrisciani]

I was more referring as a general approach more than the test itself, how to avoid to accept options that won't create any effect but will simply be silently ignored. As a first line of defense check that the option at least exists and if not return an error.

[vieux]

LGTM

[thaJeztah]

@fcrisciani anything you want me to change in this PR, or good to go?