use sdkconfig define CONFIG_ETH_ENABLED to check Ethernet availability

[Jason2866]

Description:

follow up of #22473

Checklist:

• The pull request is done against the latest development branch
• Only relevant files were touched
• Only one feature/fix was added per PR and the code change compiles without warnings
• The code change is tested and works with Tasmota core ESP8266 V.2.7.8
• The code change is tested and works with Tasmota core ESP32 V.3.1.0.241030
• I accept the CLA.

NOTE: The code change must pass CI tests. Your PR cannot be merged unless tests pass