feat+test: nic attribute modification

[dominikvagner]

connected to: #385

After extensive testing on my part and a joint investigation with @grafuls, this feature cannot be fully implemented in the current state of our lab, because of our iDRAC setup/versions. Getting a list of attributes for specific NICs is working as it should along with getting information about a specific attribute. (The same way as we do it for BIOS attributes.) Setting attributes though does not work, even if the somewhat incomplete feeling iDRAC documentation about this use case says it should for versions 5.x.x.x (testing was done against 5.10.50.0 as the newest version available to us). Neither my attempt at solving this or the reference script from Dell works. In our case the end-point accepting the setting of attributes shows no supported attributes to set.

The getting functionality was implemented and tested. The setting of attributes was made as a draft implementation supposed to completed in the future, when the environment will allow for it.