QNativeSocketEngine on *nix lacks errno handling

qnativesocketengine_unix.cpp:441

(which is related to Fix -Wimplicit-fallthrough for clang (544053) )

case EAFNOSUPPORT:
case EBADF:
case EFAULT:
case ENOTSOCK:
    socketState = QAbstractSocket::UnconnectedState;
    break;
default:
    break; //! break without handling it

If the control flow breaks there, the socket will keep in ConnectingState and try reconnecting again, which may be problematic.

In some cases which the socket failed to connect immediately (probably blocked by firewall or sth.), reconnecting will quickly drain full CPU load.

AFAIK, when using Little Snitch on macos to block network connection, connect() will fail with EOPNOTSUPP.