stream_manager: Change construction to make gcc 4.9 happy

gcc 4.9 complains about the type{ val, val } construction of
type with implicit default constructor, i.e. member = initial
declarations. gcc 5 does not (and possibly rightly so).
However, we still (implicitly) claim to support gcc 4.9 so
why not just change this particular instance.

Message-Id: <1454921328-1106-1-git-send-email-calle@scylladb.com>

streaming/stream_manager.cc

@@ -152,7 +152,7 @@ future<stream_bytes> stream_manager::get_progress_on_all_shards(UUID plan_id, gm
         [plan_id, peer] (auto& sm) {
             return sm.get_progress(plan_id, peer);
         },
-        stream_bytes{0,0},
+        stream_bytes(),
         std::plus<stream_bytes>()
     );
 }
@@ -166,7 +166,7 @@ future<stream_bytes> stream_manager::get_progress_on_all_shards(gms::inet_addres
             }
             return ret;
         },
-        stream_bytes{0,0},
+        stream_bytes(),
         std::plus<stream_bytes>()
     );
 }
@@ -182,7 +182,7 @@ future<stream_bytes> stream_manager::get_progress_on_all_shards() {
             }
             return ret;
         },
-        stream_bytes{0,0},
+        stream_bytes(),
         std::plus<stream_bytes>()
     );
 }