bth: Add IAD to BT descriptor

Bluetooth's specification defines IAD for primary controller.
While it seems that Windows and Linux can leave without this,
there is no reason TinyUSB should not provide it.

src/device/usbd.h

@@ -763,8 +763,8 @@ TU_ATTR_WEAK bool tud_vendor_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb
 #define CFG_TUD_BTH_ISO_ALT_COUNT 0
 #endif
 
-// Length of template descriptor: 30 bytes + number of ISO alternatives * 23
-#define TUD_BTH_DESC_LEN (9 + 7 + 7 + 7 + (CFG_TUD_BTH_ISO_ALT_COUNT) * (9 + 7 + 7))
+// Length of template descriptor: 38 bytes + number of ISO alternatives * 23
+#define TUD_BTH_DESC_LEN (8 + 9 + 7 + 7 + 7 + (CFG_TUD_BTH_ISO_ALT_COUNT) * (9 + 7 + 7))
 
 /* Primary Interface */
 #define TUD_BTH_PRI_ITF(_itfnum, _stridx, _ep_evt, _ep_evt_size, _ep_evt_interval, _ep_in, _ep_out, _ep_size) \
@@ -806,6 +806,8 @@ TU_ATTR_WEAK bool tud_vendor_control_xfer_cb(uint8_t rhport, uint8_t stage, tusb
 // Interface number, string index, attributes, event endpoint, event endpoint size, interval, data in, data out, data endpoint size, iso endpoint sizes
 // TODO BTH should also use IAD like CDC for composite device
 #define TUD_BTH_DESCRIPTOR(_itfnum, _stridx, _ep_evt, _ep_evt_size, _ep_evt_interval, _ep_in, _ep_out, _ep_size,...) \
+  /* Interface Associate */\
+  8, TUSB_DESC_INTERFACE_ASSOCIATION, _itfnum, 2, TUD_BT_APP_CLASS, TUD_BT_APP_SUBCLASS, TUD_BT_PROTOCOL_PRIMARY_CONTROLLER, 0,\
   TUD_BTH_PRI_ITF(_itfnum, _stridx, _ep_evt, _ep_evt_size, _ep_evt_interval, _ep_in, _ep_out, _ep_size) \
   TUD_BTH_ISO_ITFS(_itfnum + 1, _ep_in + 1, _ep_out + 1, __VA_ARGS__)