Due to a hardware limitation in ESP32, the first four bytes of some
CSI data is invalid, not the last four bytes.
Correct a mistake of CSI sub-carrier index in documentation.
1. Move channel to the first row of the table.
2. Remove the condition of HT20/HT40 for they are determined by
secondary channel.
3. Clean up the CSI table.
The WiFi station connect sequence diagram does not have any "successful" ending.
It looks like a copy-paste error, because there are two consequent `SYSTEM_EVENT_STA_DISCONNECTED` events firing with nothing happening in between.
I think the original meaning was that the last event should be `SYSTEM_EVENT_STA_CONNECTED` to signify that if all goes well, that is the event that will be fired.
Merges https://github.com/espressif/esp-idf/pull/2065
