rt2x00: clear IV's on start to fix AP mode regression

To do not brake HW restart we should keep initialization vectors data.
I assumed that on start the data is already initialized to zeros, but
that not true on some scenarios and we should clear it. So add
additional flag to check if we are under HW restart and clear IV's
data if we are not.

Patch fixes AP mode regression.

Reported-and-tested-by: Emil Karlson <jekarl@iki.fi>
Fixes: 710e6cc1 ("rt2800: do not nullify initialization vector data")
Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>