Use timeout error for TCP timeouts on unix

When a TCP connection timed out a QAbstractSocket::NetworkError was set.
To enable a more precise error handling for timeouts
QAbstractSocket::SocketTimeoutError is now set instead.
Separated ETIMEDOUT from other errors in nativeRead() and take over
responsibility for setting the error, which was previously handled by read().

Change-Id: Iccd45bdbb3d944cd160ae50c257d3256e05b1ae5
Reviewed-by: Edward Welbourne <edward.welbourne@qt.io>
Reviewed-by: David Faure <david.faure@kdab.com>

src/network/socket/qnativesocketengine_unix.cpp

@@ -1383,19 +1383,23 @@ qint64 QNativeSocketEnginePrivate::nativeRead(char *data, qint64 maxSize)
             // No data was available for reading
             r = -2;
             break;
-        case EBADF:
-        case EINVAL:
-        case EIO:
-            //error string is now set in read(), not here in nativeRead()
-            break;
         case ECONNRESET:
 #if defined(Q_OS_VXWORKS)
         case ESHUTDOWN:
 #endif
             r = 0;
             break;
-        default:
+        case ETIMEDOUT:
+            socketError = QAbstractSocket::SocketTimeoutError;
             break;
+        default:
+            socketError = QAbstractSocket::NetworkError;
+            break;
+        }
+
+        if (r == -1) {
+            hasSetSocketError = true;
+            socketErrorString = qt_error_string();
         }
     }