Forward io_uring_enter2 size argument

[fallintoplace]

Summary

This updates the io_uring_enter2 shim to pass its size argument through to the io_uring_enter syscall.

Why

The wrapper accepted a size argument, but always passed the sigset size instead. Extended-argument callers compute the size they need, so the wrapper should not discard it.

The older io_uring_enter helper still passes the sigset size when it calls io_uring_enter2, which keeps that path unchanged.

Validation

• cmake configure with Ninja and CMAKE_INSTALL_PREFIX=.build/install-io-uring-enter2-check
• cmake --build .build/cmake-io-uring-enter2-check
• cmake --install .build/cmake-io-uring-enter2-check
• Confirmed the installed CSystem io_uring.h forwards the sz argument

[FranzBusch]

This seems good to me. @Catfish-Man mind taking a look as well?

[glessard]

This is a needed fix, but we also need additional testing. I'll add that separately.