1. All espressif specific code are prefix with ESP_ 2. Define all ESP_ options in lwipopts.h 3. Remove useless code added in 8266
1. Add esp_wifi_internal.h 2. Rename system_pp_recycle_rx_pkt to esp_wifi_internal_free_rx_buffer 3. rename esp_wifi_tx_is_stop to esp_wifi_internal_tx_is_stop 4. rename ieee80211_output to esp_wifi_internal_tx