commit b661a5da upstream.

When the buffer descriptor index exceeds 2, then a TX HANG condition
will result.
Signed-off-by: Troy Tan <troy_tan@realsil.com.cn>
Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>