ifaddrs: read_attr closure returns Option, so .ok() the read_file Result

The read_attr closure is typed -> Option<Vec<u8>> and its callers use
`if let Some(...)`, but it returned read_file(...) directly, which is
Result<Vec<u8>, ()> — E0308. Map it with .ok() (Ok->Some, Err(())->None).
Fixes the relibc compile error that failed the prefix rebuild.

Co-Authored-By: Claude Opus 4.8 (1M context) <noreply@anthropic.com>

src/header/ifaddrs/mod.rs

@@ -381,7 +381,7 @@ fn enumerate_interfaces_redox() -> Result<Vec<InterfaceInfo>, ()> {
             }
             path_buf[path_len..path_len + suffix.len()].copy_from_slice(suffix);
             path_buf[path_len + suffix.len()] = 0;
-            read_file(&path_buf[..need])
+            read_file(&path_buf[..need]).ok()
         };
 
         if let Some(flags_bytes) = read_attr(b"flags") {