nimble/audio: Add subgroups information for modify operation

This commit adds subgroups info for modify source operation.
Now metadata field can be handled in scan delegator during
modify procedure.

nimble/host/audio/services/bass/include/services/bass/ble_audio_svc_bass.h

@@ -324,6 +324,10 @@ struct ble_svc_audio_bass_operation {
             /** Number of subgroups */
             uint16_t num_subgroups;
 
+            /** Subgroup entries */
+            struct ble_svc_audio_bass_subgroup
+                subgroups[BLE_SVC_AUDIO_BASS_SUB_NUM_MAX];
+
             /** BIS Synchronisation of subgroups */
             uint32_t bis_sync[BLE_SVC_AUDIO_BASS_SUB_NUM_MAX];
         } modify_source;

nimble/host/audio/src/ble_audio_scan_delegator.c

@@ -198,7 +198,8 @@ bass_modify_source_op_handler(struct ble_svc_audio_bass_operation *op, void *arg
 
     for (uint8_t i = 0; i < sync_opt->num_subgroups; i++) {
         sync_opt->subgroups[i].bis_sync = op->modify_source.bis_sync[i];
-        /* FIXME: Missing metadata in Modify Source */
+        sync_opt->subgroups[i].metadata_length = op->modify_source.subgroups[i].metadata_length;
+        sync_opt->subgroups[i].metadata = op->modify_source.subgroups[i].metadata;
     }
 
     action.type = BLE_AUDIO_SCAN_DELEGATOR_ACTION_SOURCE_MODIFY;