#381 Clarify grammar and typos in syscall section and syscall-steal.c

Fix grammatical errors and typos in the syscall description section and the syscall-steal.c example file to improve readability.

---

Summary by cubic

Clarifies terminology and fixes typos in the syscall section and example comments for accuracy; no runtime or build changes.

• In lkmpg.tex, explains that the syscall dispatcher changed from an indirect call table to a switch to mitigate BHI attacks.
• In examples/syscall-steal.c, corrects that sys_openat is a static function (not a variable), fixes “wreak havoc,” and clarifies why the original call pointer is retained.