1. If L2_TO_L3_RX_BUF_MODE is not selected, we must assign l2_owner explictly before we call pbuf_free.
2. free intr resource in esp_eth_deinit
Closes https://github.com/espressif/esp-idf/issues/2670
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]
1. change static emac-dma memory to dynamic
2. add esp_eth_deinit
3. modify ethernet example
4. add testcase for ethernet deinit function
5. GPIO0 could not output the 50MHz clock to PHY, so remove this configuration
