rtw_write_port stores a queue index in pxmitbuf->flags before submitting
an urb. The urb completion function reads the flags. All it needs is the
info if the high queue was used or not.

We can replace the flags with a boolean high_queue variable.
Signed-off-by: Martin Kaiser <martin@kaiser.cx>
Tested-by: Philipp Hortmann <philipp.g.hortmann@gmail.com> # Edimax N150
Link: https://lore.kernel.org/r/20230207192319.294203-6-martin@kaiser.cxSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>