prepare/netdevsim: physical addres patch + newer kernel support

Make netdevsim devices report random MAC address created during netdevsim setup as its physical address (benefitial to GUI applications, as it does not report NULL as MAC address).

Newer kernels does not need ethtools patch anymore, do just physical address patch.

Add setup argument: number of devices to create.

@RunTests:ethtool_features_ring,ethtool_features_coal