db::commitlog::descriptor::descriptor(filename): pass a filename as a const ref

Avoid not needed copy by passing a file name as a reference.

Signed-off-by: Vlad Zolotarov <vladz@scylladb.com>

db/commitlog/commitlog.hh

@@ -139,7 +139,7 @@ public:
         descriptor(const descriptor&) = default;
         descriptor(segment_id_type i, uint32_t v = 1);
         descriptor(replay_position p);
-        descriptor(sstring filename);
+        descriptor(const sstring& filename);
 
         sstring filename() const;
         operator replay_position() const;