Correction of the type in sockopt_impl macro

Author: Fensteer

src/sys/socket/sockopt.rs

@@ -154,7 +154,7 @@ macro_rules! sockopt_impl {
         sockopt_impl!(Both, $name, $level, $flag, usize, GetUsize, SetUsize);
     };
 
-    (Both, $name:ident, $level:path, $flag:path, usize) => {
+    (Both, $name:ident, $level:path, $flag:path, CString) => {
         sockopt_impl!(Both, $name, $level, $flag, CString, GetCString, SetCString);
     };