kernel: keep legacy throne tracker as an option

kernel: keep legacy throne tracker as an option

This change restores older throne tracker that uses packages.list scanning
to track app UIDs. It's intended for ultra-legacy Linux 3.X kernels that
experience deadlocks or crashes with the newer implementation due to issues
in user_data_actor().

We have to remember that the whole iterate_dir, and filldir subsystem is way
different on 3.X.

Changes:
- CONFIG_KSU_THRONE_TRACKER_LEGACY in Kconfig
- conditional compilation in Makefile
- throne_tracker_legacy.c which keeps the old implementation

Enable this option if newer throne tracker (tiann #2757crashes on you.)

Co-authored-by: backslashxx <118538522+backslashxx@users.noreply.github.com>

kernel/Kconfig

@@ -8,6 +8,15 @@ config KSU
 	    To compile as a module, choose M here: the
 	    module will be called kernelsu.
 
+config KSU_THRONE_TRACKER_LEGACY
+	bool "Use legacy throne tracker (packages.list scanning)"
+	depends on KSU
+	default n
+	help
+	  Use legacy throne tracker that scans packages.list for app UIDs.
+	  This is kept for Ultra-Legacy Linux 3.X kernels which are prone to deadlocks.
+	  Enable this if default scanning deadlocks/crashes on you.
+
 config KSU_DEBUG
 	  bool "KernelSU debug mode"
 	  depends on KSU