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

Summary:
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.

This concludes a backport of [[bitcoin/bitcoin#23173 | core#23173]]
bitcoin/bitcoin@0fdb619

Depends on D12235

Test Plan: `ninja all check-all`

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Differential Revision: https://reviews.bitcoinabc.org/D12236

Author: jnewbery

src/net_processing.cpp

@@ -3133,9 +3133,6 @@ void PeerManagerImpl::ProcessOrphanTx(const Config &config,
             break;
         }
     }
-    CChainState &active_chainstate = m_chainman.ActiveChainstate();
-    m_mempool.check(active_chainstate.CoinsTip(),
-                    active_chainstate.m_chain.Height() + 1);
 }
 
 bool PeerManagerImpl::PrepareBlockFilterRequest(
@@ -4367,9 +4364,6 @@ void PeerManagerImpl::ProcessMessage(
         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.ForgetInvId(tx.GetId());

src/validation.cpp

@@ -4287,9 +4287,12 @@ ChainstateManager::ProcessTransaction(const CTransactionRef &tx,
     // making AcceptToMemoryPool take a CChainParams instead of a Config.
     // This avoids passing an extra Config argument to this function that will
     // be removed soon.
-    return AcceptToMemoryPool(active_chainstate, ::GetConfig(),
-                              *active_chainstate.m_mempool, tx,
-                              /*bypass_limits=*/false, test_accept);
+    auto result = AcceptToMemoryPool(active_chainstate, ::GetConfig(),
+                                     *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, const CChainParams &params,