Do not process blocks in CDeterministicMNManager before dip3 activation (#2698)

* Do not process blocks in CDeterministicMNManager before dip3 activation

This should save us some cpu/disk on initial sync/reindex

* Write initial snapshot on dip3 activation

Author: UdjinM6

src/evo/deterministicmns.cpp

@@ -447,6 +447,13 @@ CDeterministicMNManager::CDeterministicMNManager(CEvoDB& _evoDb) :
 
 bool CDeterministicMNManager::ProcessBlock(const CBlock& block, const CBlockIndex* pindex, CValidationState& _state, bool fJustCheck)
 {
+    AssertLockHeld(cs_main);
+
+    bool fDIP0003Active = VersionBitsState(pindex->pprev, Params().GetConsensus(), Consensus::DEPLOYMENT_DIP0003, versionbitscache) == THRESHOLD_ACTIVE;
+    if (!fDIP0003Active) {
+        return true;
+    }
+
     CDeterministicMNList oldList, newList;
     CDeterministicMNListDiff diff;
 
@@ -473,7 +480,7 @@ bool CDeterministicMNManager::ProcessBlock(const CBlock& block, const CBlockInde
         diff = oldList.BuildDiff(newList);
 
         evoDb.Write(std::make_pair(DB_LIST_DIFF, diff.blockHash), diff);
-        if ((nHeight % SNAPSHOT_LIST_PERIOD) == 0) {
+        if ((nHeight % SNAPSHOT_LIST_PERIOD) == 0 || oldList.GetHeight() == -1) {
             evoDb.Write(std::make_pair(DB_LIST_SNAPSHOT, diff.blockHash), newList);
             LogPrintf("CDeterministicMNManager::%s -- Wrote snapshot. nHeight=%d, mapCurMNs.allMNsCount=%d\n",
                 __func__, nHeight, newList.GetAllMNsCount());