Avoid calling BanMan::SweepBanned() twice in a row

src/banman.cpp

@@ -43,16 +43,15 @@ void BanMan::DumpBanlist()
     static Mutex dump_mutex;
     LOCK(dump_mutex);
 
+    banmap_t banmap;
     {
         LOCK(m_cs_banned);
         SweepBanned();
         if (!BannedSetIsDirty()) return;
+        banmap = m_banned;
     }
 
     int64_t n_start = GetTimeMillis();
-
-    banmap_t banmap;
-    GetBanned(banmap);
     if (m_ban_db.Write(banmap)) {
         SetBannedSetDirty(false);
     }