Problem: plain_server_t duplicates zap_client_t::send_zap_request

Solution: Use zap_client_t::send_zap_request

src/plain_server.hpp

@@ -32,6 +32,7 @@
 
 #include "mechanism.hpp"
 #include "options.hpp"
+#include "zap_client.hpp"
 
 namespace zmq
 {
@@ -71,6 +72,8 @@ namespace zmq
 
         const std::string peer_address;
 
+        zap_client_t zap_client;
+
         //  Status code as received from ZAP handler
         std::string status_code;