iq: Implement the Iq*Payload traits on every possible payload.

src/ping.rs

@@ -5,8 +5,12 @@
 // License, v. 2.0. If a copy of the MPL was not distributed with this
 // file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+use iq::IqGetPayload;
+
 generate_empty_element!(Ping, "ping", PING);
 
+impl IqGetPayload for Ping {}
+
 #[cfg(test)]
 mod tests {
     use super::*;