[RFKILL]: Add support for hardware-only rfkill buttons

Buttons that work directly on hardware cannot support
the "user_claim" functionality. Add a flag to signal
this and return -EOPNOTSUPP in this case.
b43 is such a device.

Signed-off-by: Michael Buesch <mb@bu3sch.de>
Acked-by: Ivo van Doorn <IvDoorn@gmail.com>
Signed-off-by: John W. Linville <linville@tuxdriver.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
diff --git a/net/rfkill/rfkill.c b/net/rfkill/rfkill.c
index a8c5e0b..51d151c 100644
--- a/net/rfkill/rfkill.c
+++ b/net/rfkill/rfkill.c
@@ -190,6 +190,10 @@
 	if (error)
 		return error;
 
+	if (rfkill->user_claim_unsupported) {
+		error = -EOPNOTSUPP;
+		goto out_unlock;
+	}
 	if (rfkill->user_claim != claim) {
 		if (!claim)
 			rfkill_toggle_radio(rfkill,
@@ -197,9 +201,10 @@
 		rfkill->user_claim = claim;
 	}
 
+out_unlock:
 	mutex_unlock(&rfkill_mutex);
 
-	return count;
+	return error ? error : count;
 }
 
 static struct device_attribute rfkill_dev_attrs[] = {