message: Don't request a mempool sync unless our chain is nearly synced
  We don't process INV's for transactions and then request transactions
  before IBD is complete so there's no need to do any mempool syncing
  either.
diff: @@ -2288,7 +2288,7 @@ void ThreadMessageHandler()
  {
  // select node from whom to request mempool sync
  CNode *syncPeer = SelectMempoolSyncPeer(vNodesCopy);
  - if (!(syncPeer == nullptr))
  + if (syncPeer && IsChainNearlySyncd())
  requester.RequestMempoolSync(syncPeer);
  }
  