ci: Use proper NuttX sample for testing

Select example app from NimBLE tree instead of Nuttx upstream. Also
properly tune build for PR hash and include upstream NimBLE
configuration with sample. This is due to NuttX not following our
master branch but selected snapshots/releases with custom
configuration.

Author: sjanc

.github/workflows/build_ports.yml

@@ -87,5 +87,9 @@ jobs:
              git clone --depth=1 https://github.com/apache/nuttx.git nuttx-build/nuttx
              git clone --depth=1 https://github.com/apache/nuttx-apps nuttx-build/apps
              ./nuttx-build/nuttx/tools/configure.sh -l nrf52840-dk:sdc_nimble
-             sed -i 's|CONFIG_NIMBLE_REF :=.*|CONFIG_NIMBLE_REF := ${{ github.sha }}|' nuttx-build/apps/wireless/bluetooth/nimble/Makefile
+             kconfig-tweak --file nuttx-build/nuttx/.config --set-str NIMBLE_REF ${{ github.sha }}
+             kconfig-tweak --file nuttx-build/nuttx/.config --enable NIMBLE_PORTING_EXAMPLE
+             echo '#include "../../../../mynewt-nimble/porting/examples/nuttx/include/syscfg/syscfg.h"'\
+               >> nuttx-build/apps/wireless/bluetooth/nimble/include/syscfg/syscfg.h
+             make -C nuttx-build/nuttx olddefconfig
              make -C nuttx-build/nuttx