iwlegacy: enable only rfkill interrupt when device is down

Add two below iwlwifi commits to iwlegacy:

commit 554d1d02
Author: Stanislaw Gruszka <sgruszka@redhat.com>
Date:   Thu Dec 23 12:38:21 2010 +0100

    iwlagn: enable only rfkill interrupt when device is down

commit 3dd823e6
Author: Don Fry <donald.h.fry@intel.com>
Date:   Sun Feb 6 09:29:45 2011 -0800

    iwlagn: Re-enable RF_KILL interrupt when down

Signed-off-by: Stanislaw Gruszka <sgruszka@redhat.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>