Bluetooth: Fix Kconfig issue with RFKILL integration

Since the re-write of the RFKILL subsystem it is no longer good to just
select RFKILL, but it is important to add a proper depends on rule.

Based on a report by Alexander Beregalov <a.beregalov@gmail.com>

Signed-off-by: Marcel Holtmann <marcel@holtmann.org>
diff --git a/net/bluetooth/Kconfig b/net/bluetooth/Kconfig
index 7725da9..59fdb1d 100644
--- a/net/bluetooth/Kconfig
+++ b/net/bluetooth/Kconfig
@@ -3,8 +3,9 @@
 #
 
 menuconfig BT
-	depends on NET && !S390
 	tristate "Bluetooth subsystem support"
+	depends on NET && !S390
+	depends on RFKILL || !RFKILL
 	help
 	  Bluetooth is low-cost, low-power, short-range wireless technology.
 	  It was designed as a replacement for cables and other short-range