v2.5.1 to slow SPI clock to `8MHz` and select `SPI_MODE0` for old W5100 shield using SAMD Zero and default to `W5100` to be safe in examples

Releases v2.5.1

1. Slow SPI clock to 8MHz and select SPI_MODE0 for old W5100 shield using SAMD Zero. Check AdvancedWebServer example give me wrong ip HTTP EthernetWebServer is @ IP : 0.0.0.0 #62
2. Default to W5100 to be safe. To change if using W5200, W5500, W5100s or testing faster SPI clock speeds