ksud: use move mount instead of remount for stock mounts

Because some stock mounts are difficult to remount it back, so we bind mount it to somewhere else before overlayfs mount. And then use move mount to mount it back.

userspace/ksud/src/defs.rs

@@ -5,6 +5,7 @@ pub const WORKING_DIR: &str = concatcp!(ADB_DIR, "ksu/");
 pub const BINARY_DIR: &str = concatcp!(WORKING_DIR, "bin/");
 
 pub const KSURC_PATH: &str = concatcp!(WORKING_DIR, ".ksurc");
+pub const STOCK_MNT_ROOT: &str = concatcp!(WORKING_DIR, ".mnt");
 pub const DAEMON_PATH: &str = concatcp!(ADB_DIR, "ksud");
 
 #[cfg(target_os = "android")]