fix block_tip

Author: alexanderwiederin

src/lib.rs

@@ -415,7 +415,7 @@ unsafe extern "C" fn kn_user_data_destroy_wrapper(user_data: *mut c_void) {
 unsafe extern "C" fn kn_block_tip_wrapper(
     user_data: *mut c_void,
     state: btck_SynchronizationState,
-    entry: *mut btck_BlockTreeEntry,
+    entry: *const btck_BlockTreeEntry,
     verification_progress: f64,
 ) {
     let holder = &*(user_data as *mut KernelNotificationInterfaceCallbacks);