As a system administrator, I want Nmstate to support the setting and verification of private flags for network interfaces, using NetworkManager to configure the flags via ethtool, so that I can enable and manage vendor-specific settings on NICs through the standard Nmstate interface. Acceptance criteria Given a system with a NIC that supports vendor-specific private flags, When the system administrator configures a private flag using Nmstate, Then, Nmstate should communicate with NetworkManager to apply the flag using ethtool, and the flag's current status should be correctly displayed when fetching the device status through Nmstate. Definition of Done: The implementation meets the acceptance criteria Integration tests are written and pass The fix is part of a downstream build attached to an errata