Set TCP_NODELAY on P2P sockets.

Nagle appears to be a significant contributor to latency now that the static
 sleeps are gone.  Most of our messages are relatively large compared to
 IP + TCP so I do not expect this to create enormous overhead.

This may also reduce traffic burstyness somewhat.

Conflicts:
	src/net.cpp

Rebased-From: a4e28b3d1e
Github-Pull: #6867

src/net.cpp

@@ -869,6 +869,15 @@ void ThreadSocketHandler()
                 }
                 else
                 {
+                    // According to the internet TCP_NODELAY is not carried into accepted sockets
+                    // on all platforms.  Set it again here just to be sure.
+                    int set = 1;
+#ifdef WIN32
+                    setsockopt(hSocket, IPPROTO_TCP, TCP_NODELAY, (const char*)&set, sizeof(int));
+#else
+                    setsockopt(hSocket, IPPROTO_TCP, TCP_NODELAY, (void*)&set, sizeof(int));
+#endif
+
                     CNode* pnode = new CNode(hSocket, addr, "", true);
                     pnode->AddRef();
                     pnode->fWhitelisted = whitelisted;
@@ -1508,8 +1517,11 @@ bool BindListenPort(const CService &addrBind, string& strError, bool fWhiteliste
     // Allow binding if the port is still in TIME_WAIT state after
     // the program was closed and restarted.
     setsockopt(hListenSocket, SOL_SOCKET, SO_REUSEADDR, (void*)&nOne, sizeof(int));
+    // Disable Nagle's algorithm
+    setsockopt(hListenSocket, IPPROTO_TCP, TCP_NODELAY, (void*)&nOne, sizeof(int));
 #else
     setsockopt(hListenSocket, SOL_SOCKET, SO_REUSEADDR, (const char*)&nOne, sizeof(int));
+    setsockopt(hListenSocket, IPPROTO_TCP, TCP_NODELAY, (const char*)&nOne, sizeof(int));
 #endif
 
     // Set to non-blocking, incoming connections will also inherit this