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>

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