message: [backbone-router] fix OT options for Backone Router
diff: @@ -96,9 +96,9 @@ if (OTBR_BACKBONE_ROUTER)
  target_compile_definitions(otbr-config INTERFACE
  OTBR_ENABLE_BACKBONE_ROUTER=1
  )
  - set(OT_THREAD_VERSION 1.2)
  - set(OT_BACKBONE_ROUTER ON)
  - set(OT_SERVICE ON)
  + set(OT_THREAD_VERSION 1.2 CACHE STRING "Backbone Router requires Thread 1.2 or higher" FORCE)
  + set(OT_BACKBONE_ROUTER ON CACHE BOOL "Enable Backbone Router feature in OpenThread" FORCE)
  + set(OT_SERVICE ON CACHE BOOL "Backbone Router requires Thread network service" FORCE)
  endif()
  if(OTBR_DBUS)
  