[validation] Always call mempool.check() after processing a new transaction

CTxMemPool::check() will carry out internal consistency checks 1/n times,
where n is set by the `-checkmempool` configuration option. By default,
mempool consistency checks are disabled entirely on mainnet.

Therefore, this change has no effect on mainnet nodes running with
default configuration. It simply removes the responsibility to trigger
mempool consistency checks from net_processing.

Author: jnewbery

src/net_processing.cpp

@@ -2300,8 +2300,6 @@ void PeerManagerImpl::ProcessOrphanTx(std::set<uint256>& orphan_work_set)
             break;
         }
     }
-    CChainState& active_chainstate = m_chainman.ActiveChainstate();
-    m_mempool.check(active_chainstate.CoinsTip(), active_chainstate.m_chain.Height() + 1);
 }
 
 bool PeerManagerImpl::PrepareBlockFilterRequest(CNode& peer,
@@ -3264,8 +3262,6 @@ void PeerManagerImpl::ProcessMessage(CNode& pfrom, const std::string& msg_type,
         const TxValidationState& state = result.m_state;
 
         if (result.m_result_type == MempoolAcceptResult::ResultType::VALID) {
-            CChainState& active_chainstate = m_chainman.ActiveChainstate();
-            m_mempool.check(active_chainstate.CoinsTip(), active_chainstate.m_chain.Height() + 1);
             // As this version of the transaction was acceptable, we can forget about any
             // requests for it.
             m_txrequest.ForgetTxHash(tx.GetHash());

src/validation.cpp

@@ -3429,7 +3429,9 @@ MempoolAcceptResult ChainstateManager::ProcessTransaction(const CTransactionRef&
         state.Invalid(TxValidationResult::TX_NO_MEMPOOL, "no-mempool");
         return MempoolAcceptResult::Failure(state);
     }
-    return AcceptToMemoryPool(active_chainstate, *active_chainstate.m_mempool, tx, /*bypass_limits=*/ false, test_accept);
+    auto result = AcceptToMemoryPool(active_chainstate, *active_chainstate.m_mempool, tx, /*bypass_limits=*/ false, test_accept);
+    active_chainstate.m_mempool->check(active_chainstate.CoinsTip(), active_chainstate.m_chain.Height() + 1);
+    return result;
 }
 
 bool TestBlockValidity(BlockValidationState& state,