Various unix socket fixes (+socketpair!)

src/header/sys_un/mod.rs

@@ -5,3 +5,12 @@ pub struct sockaddr_un {
     pub sun_family: sa_family_t,
     pub sun_path: [c_char; 108],
 }
+
+impl sockaddr_un {
+    pub fn path_len(&self) -> usize {
+        let base = self as *const _ as usize;
+        let path = &self.sun_path as *const _ as usize;
+        trace!("base: {:#X}, path: {:#X}", base, path);
+        path - base
+    }
+}