iwlegacy: fix channel switch locking

iwlegacy: fix channel switch locking

commit 51e65257142a87fe46a1ce5c35c86c5baf012614 upstream.

We use priv->mutex to avoid race conditions between chswitch_done()
and mac_channel_switch(), when marking channel switch in
progress. But chswitch_done() can be called in atomic context
from rx_csa() or with mutex already taken from commit_rxon().

To fix remove mutex from chswitch_done() and use atomic bitops
for marking channel switch pending.

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>