Increased LAN8720 ETH-PHY reset assertion time (IDFGH-6018)

Increase reset assertion time from 100µs (as specified minimum in the datasheet) to 150µs.
Some specimen of the LAN8720 need the reset signal asserted longer than 100µs to initialise properly. Otherwise they are in a zombie state where they are establishing and loosing an Ethernet link once in a seconds interval.

components/esp_eth/src/esp_eth_phy_lan87xx.c

@@ -337,7 +337,8 @@ static esp_err_t lan87xx_reset_hw(esp_eth_phy_t *phy)
         esp_rom_gpio_pad_select_gpio(lan87xx->reset_gpio_num);
         gpio_set_direction(lan87xx->reset_gpio_num, GPIO_MODE_OUTPUT);
         gpio_set_level(lan87xx->reset_gpio_num, 0);
-        esp_rom_delay_us(100); // insert min input assert time
+        /* assert nRST signal on LAN87xx a little longer than the minimum specified in datasheet */
+        esp_rom_delay_us(150);
         gpio_set_level(lan87xx->reset_gpio_num, 1);
     }
     return ESP_OK;