net: Move IsSelectableSocket check into socket creation

We use select in ConnectSocketDirectly, so this check needs to happen before
that.

IsSelectableSocket will not be relevant after upcoming changes to remove select.

src/net.cpp

@@ -446,24 +446,19 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
         SplitHostPort(std::string(pszDest), port, host);
         connected = ConnectThroughProxy(proxy, host, port, hSocket, nConnectTimeout, nullptr);
     }
-    if (connected) {
-        if (!IsSelectableSocket(hSocket)) {
-            LogPrintf("Cannot create connection: non-selectable socket created (fd >= FD_SETSIZE ?)\n");
-            CloseSocket(hSocket);
-            return nullptr;
-        }
-
-        // Add node
-        NodeId id = GetNewNodeId();
-        uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE).Write(id).Finalize();
-        CAddress addr_bind = GetBindAddress(hSocket);
-        CNode* pnode = new CNode(id, nLocalServices, GetBestHeight(), hSocket, addrConnect, CalculateKeyedNetGroup(addrConnect), nonce, addr_bind, pszDest ? pszDest : "", false);
-        pnode->AddRef();
-
-        return pnode;
+    if (!connected) {
+        CloseSocket(hSocket);
+        return nullptr;
     }
 
-    return nullptr;
+    // Add node
+    NodeId id = GetNewNodeId();
+    uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE).Write(id).Finalize();
+    CAddress addr_bind = GetBindAddress(hSocket);
+    CNode* pnode = new CNode(id, nLocalServices, GetBestHeight(), hSocket, addrConnect, CalculateKeyedNetGroup(addrConnect), nonce, addr_bind, pszDest ? pszDest : "", false);
+    pnode->AddRef();
+
+    return pnode;
 }
 
 void CConnman::DumpBanlist()

src/netbase.cpp

@@ -465,6 +465,12 @@ SOCKET CreateSocket(const CService &addrConnect)
     if (hSocket == INVALID_SOCKET)
         return INVALID_SOCKET;
 
+    if (!IsSelectableSocket(hSocket)) {
+        CloseSocket(hSocket);
+        LogPrintf("Cannot create connection: non-selectable socket created (fd >= FD_SETSIZE ?)\n");
+        return INVALID_SOCKET;
+    }
+
 #ifdef SO_NOSIGPIPE
     int set = 1;
     // Different way of disabling SIGPIPE on BSD