Added flag to control whether enable base64 in BLE advertisement header

PiperOrigin-RevId: 513924031

internal/platform/feature_flags.h

@@ -47,6 +47,8 @@ class FeatureFlags {
     bool support_multiple_bwu_mediums = true;
     // Ble v2/v1 switch flag: the flag will be removed once v2 refactor is done.
     bool support_ble_v2 = false;
+    // Controls BLE advertisement data format in base64 or not.
+    bool enable_ble_v2_advertisement_base64_encoding = false;
     // Allows the code to change the bluetooth radio state
     bool enable_set_radio_state = false;
     // If the feature is enabled, medium connection will timeout when cannot