This commit adds support for sending Vendor Specific HCI commands and handling Vendor Specific HCI
Events in the Nimble stack. It also includes the necessary configuration options and APIs to handle
these commands and events.
The following changes were made:
- Added configuration option to enable support for VSC and VSE
- Added API to send Vendor Specific HCI commands
- Added example code for using the Set RSSI VSC for Power Control
This commit also includes some minor code improvements and bug fixes
- Add menuconfig option for NimBLE host flow control
- Include changes in `blecent` example from upstream PR!702
- add ble_hs_lock in ble_gap_unpair Upstream PR!584
- ble_hs_hci_rx_evt, upstream PR!738
Closes https://github.com/espressif/esp-idf/issues/4243