Clean up kernel code (#2898)

1) Fix memory leak of callback head in allowlist.c
2) Remove duplicated logic and incorrect log in kernel_umount.c
3) Prevent sleep in kprobe context in ksud.c
4) Remove useless is_unsupported_uid, use euid for security enhance,
   add FIXME in setuid_hook.c
5) Remove useless fd argument for execve hook, fix incorrent pointer
   usage in syscall_hook_manager.c and sucompat.c
6) Use correct errno in supercalls.c

---------

Co-authored-by: Ylarod <me@ylarod.cn>

kernel/allowlist.c

@@ -402,6 +402,7 @@ close_file:
     filp_close(fp, 0);
 unlock:
     mutex_unlock(&allowlist_mutex);
+    kfree(_cb);
 }
 
 void persistent_allow_list()