kernel: add wrapper for creds, refine disable_seccomp, revert some changes (#131)

1. Wrapper for creds:
* Some older kernel does not have {.val}, so, for nicer compatibility support and clean code,
make some wrapper for credential use.
* After this change, do not use current_uid().val, instead, use ksu_current_uid(). For more
info, check kernel/include/ksu_creds.h.

2. Refine disable_seccomp (need to add k6.11+ support)
https://github.com/tiann/KernelSU/pull/2708
https://github.com/tiann/KernelSU/issues/2706

3. Revert "Handle unmount for isolated process correctly"
Reason: https://github.com/tiann/KernelSU/pull/2696#issuecomment-3181866301

4. consolidate most of the gaps

Co-authored-by: Wang Han <416810799@qq.com>

kernel/setup.sh

@@ -41,8 +41,7 @@ setup_kernelsu() {
     echo "[+] Setting up KernelSU..."
     # Clone the repository and rename it to KernelSU
     if [ ! -d "$GKI_ROOT/KernelSU" ]; then
-        git clone https://github.com/SukiSU-Ultra/SukiSU-Ultra SukiSU-Ultra
-        mv SukiSU-Ultra KernelSU
+        git clone https://github.com/SukiSU-Ultra/SukiSU-Ultra KernelSU
         echo "[+] Repository cloned and renamed to KernelSU."
     fi
     cd "$GKI_ROOT/KernelSU"