refactor(sync): add leader transfer callback

source/libs/sync/src/syncMain.c

@@ -2601,6 +2601,10 @@ const char* syncStr(ESyncState state) {
 int32_t syncDoLeaderTransfer(SSyncNode* ths, SRpcMsg* pRpcMsg, SSyncRaftEntry* pEntry) {
   SyncLeaderTransfer* pSyncLeaderTransfer = syncLeaderTransferFromRpcMsg2(pRpcMsg);
 
+  if (ths->state != TAOS_SYNC_STATE_FOLLOWER) {
+    syncNodeEventLog(ths, "I am not follower, can not do leader transfer");
+    return 0;
+  }
   syncNodeEventLog(ths, "do leader transfer");
 
   bool sameId = syncUtilSameId(&(pSyncLeaderTransfer->newLeaderId), &(ths->myRaftId));