Logging in series of examples has misuse of "%d" instead of type-appropriate format specifiers.
Fix by changing "%d" to PRIxx macros corresponding to type.
Remove -Wno-format compile flag in those examples that are affected.
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]
