net: make vRecvMsg a list so that we can use splice()

src/net.cpp

@@ -1859,7 +1859,7 @@ void CConnman::ThreadMessageHandler()
 
                     if (pnode->nSendSize < GetSendBufferSize())
                     {
-                        if (!pnode->vRecvGetData.empty() || (!pnode->vRecvMsg.empty() && pnode->vRecvMsg[0].complete()))
+                        if (!pnode->vRecvGetData.empty() || (!pnode->vRecvMsg.empty() && pnode->vRecvMsg.front().complete()))
                         {
                             fSleep = false;
                         }

src/net.h

@@ -605,7 +605,7 @@ public:
     CCriticalSection cs_vSend;
 
     std::deque<CInv> vRecvGetData;
-    std::deque<CNetMessage> vRecvMsg;
+    std::list<CNetMessage> vRecvMsg;
     CCriticalSection cs_vRecvMsg;
     uint64_t nRecvBytes;
     int nRecvVersion;

src/net_processing.cpp

@@ -2471,7 +2471,7 @@ bool ProcessMessages(CNode* pfrom, CConnman& connman, std::atomic<bool>& interru
     // this maintains the order of responses
     if (!pfrom->vRecvGetData.empty()) return fOk;
 
-    std::deque<CNetMessage>::iterator it = pfrom->vRecvMsg.begin();
+    auto it = pfrom->vRecvMsg.begin();
     while (!pfrom->fDisconnect && it != pfrom->vRecvMsg.end()) {
         // Don't bother if send buffer is too full to respond anyway
         if (pfrom->nSendSize >= nMaxSendBufferSize)