large_data_handler: propagate a future out of stop()

stop() will close a semaphore in a followup patch, so it needs to return a
future.

Signed-off-by: Rafael Ávila de Espíndola <espindola@scylladb.com>

database.cc

@@ -1665,12 +1665,14 @@ future<> stop_database(sharded<database>& sdb) {
         });
     }).then([&sdb] {
         return sdb.invoke_on_all([](database& db) {
-            db.stop_large_data_handler();
+            return db.stop_large_data_handler();
         });
     });
 }
 
-void database::stop_large_data_handler() { _large_data_handler->stop(); }
+future<> database::stop_large_data_handler() {
+    return _large_data_handler->stop();
+}
 
 future<>
 database::stop() {

database.hh

@@ -1373,7 +1373,7 @@ public:
     future<> stop();
     future<> close_tables(table_kind kind_to_close);
 
-    void stop_large_data_handler();
+    future<> stop_large_data_handler();
     unsigned shard_of(const dht::token& t);
     unsigned shard_of(const mutation& m);
     unsigned shard_of(const frozen_mutation& m);

db/large_data_handler.hh

@@ -53,9 +53,10 @@ public:
     // Once large_data_handler is stopped it will ignore requests to update system.large_partitions. Any futures already
     // returned must be waited for by the caller.
     bool stopped() const { return _stopped; }
-    void stop() {
+    future<> stop() {
         assert(!stopped());
         _stopped = true;
+        return make_ready_future<>();
     }
 
     future<> maybe_record_large_rows(const sstables::sstable& sst, const sstables::key& partition_key,