Claude review: selftests/net: devmem.py: add check_rx_large_niov

[Claude Code Review Bot <claude-review@example.com>]

Patch Review

**Substantive issue:**

1. **Python string escape vs shell escape in `data_pipe`:**

```python
data_pipe = (f"yes $(echo -e \x01\x02\x03\x04\x05\x06) | "
             f"head -c {size} | {socat}")
```

The `\x01` through `\x06` are Python escape sequences, producing literal control-character bytes (SOH, STX, etc.) embedded in the shell command string. While this technically works (echo -e will pass through raw bytes that aren't backslash sequences), it's fragile -- some shells or SSH transports may not handle embedded control characters in command strings reliably. Consider using raw strings (`r"\x01..."`) so that `echo -e` receives the actual backslash-escape sequences, or use a different approach for generating binary test data (e.g., `dd if=/dev/urandom bs={size} count=1`).

**Minor:**

2. **Probe caching for `rx_buf_size` variants** in `require_devmem()` is well-designed -- it caches per-size probe results to avoid redundant probes across the sweep.

3. **Test coverage is good** -- the sweep `[1024, 4096, 8192, 16384, 32768, 65536]` nicely brackets the 16384 niov boundary (sub-niov, exact-niov, 2x, 4x).

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Generated by Claude Code Patch Reviewer