1. Add command for Ethernet based on console component.
2. Make cmd_system and iperf a component that can be referenced by other examples
3. Add "version" command to cmd_system.c
4. Clean up the README.md in all ethernet examples[TW#26525]
This change adds a check for compatibility between the nvs version
found on nvs flash and the one assumed by running code during nvs
initialization. Any mismatch is reported to the user using new error
code ESP_ERR_NVS_NEW_VERSION_FOUND.