rt2800: increase TX timeout

When medium is busy or frames have to be resend, it takes time to send
the frames and get TX status from hardware. For some really bad medium
conditions it can take seconds. Patch change TX status timeout to give
HW more time to provide it, however 500ms is not enough for bad
conditions. In the future this timeout should be removed and replaced
with proper watchdog mechanism.

Increase flush timeout accordingly as well.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>