Add rust binding for s2n_set_config_send_buffer_size (#3582)

* Add rust binding for s2n_set_config_send_buffer_size

Useful for netbench testing of the send buffer size.

* Fix format

bindings/rust/s2n-tls/src/config.rs

@@ -400,6 +400,11 @@ impl Builder {
         Ok(self)
     }
 
+    pub fn set_send_buffer_size(&mut self, size: u32) -> Result<&mut Self, Error> {
+        unsafe { s2n_config_set_send_buffer_size(self.as_mut_ptr(), size).into_result() }?;
+        Ok(self)
+    }
+
     /// Set a custom callback function which is run after parsing the client hello.
     pub fn set_client_hello_callback<T: 'static + ClientHelloCallback>(
         &mut self,