[vio] PS-5327 proxy protocol-related memory leak at shutdown

The Problem:
When proxy protocol is enabled, MySQL won't cleanup
vio_pp_networks variable at shutdown.

Solution:
Cleanup allocated networks at shutdown.
Enhanced proxy_protocol test to cover this scenario.

include/violite.h

@@ -190,6 +190,7 @@ struct st_vio_network {
 };
 
 void vio_proxy_protocol_add(const st_vio_network &net) noexcept;
+void vio_proxy_cleanup() noexcept;
 /* setsockopt TCP_NODELAY at IPPROTO_TCP level, when possible */
 int vio_fastsend(MYSQL_VIO vio);
 /* setsockopt SO_KEEPALIVE at SOL_SOCKET level, when possible */

mysql-test/r/proxy_protocol.result

@@ -0,0 +1,7 @@
+SELECT @@proxy_protocol_networks;
+@@proxy_protocol_networks
+*
+# An unproxied client connection should be rejected if proxying enabled on the server
+Got one of the listed errors
+# PS-5327 proxy protocol-related memory leak at shutdown
+# restart

mysql-test/t/proxy_protocol.test

@@ -0,0 +1,11 @@
+SELECT @@proxy_protocol_networks;
+
+--echo # An unproxied client connection should be rejected if proxying enabled on the server
+--disable_query_log
+--error ER_BAD_HOST_ERROR,CR_SERVER_LOST
+connect (err,"127.0.0.1",root,,,$MASTER_MYPORT,);
+--enable_query_log
+
+--echo # PS-5327 proxy protocol-related memory leak at shutdown
+# Restart the server
+--source include/restart_mysqld.inc

vio/vio.cc

@@ -560,7 +560,10 @@ void vio_delete(Vio *vio) { internal_vio_delete(vio); }
   components below it when application finish
 
 */
-void vio_end() { vio_ssl_end(); }
+void vio_end() {
+  vio_ssl_end();
+  vio_proxy_cleanup();
+}
 
 struct vio_string {
   const char *m_str;

vio/viosocket.cc

@@ -751,6 +751,8 @@ void vio_proxy_protocol_add(const struct st_vio_network &net) noexcept {
   memcpy(&vio_pp_networks[vio_pp_networks_nb - 1], &net, sizeof(net));
 }
 
+void vio_proxy_cleanup() noexcept { my_free(vio_pp_networks); }
+
 /* Check whether a connection from this source address must provide the proxy
    protocol header */
 static bool vio_client_must_be_proxied(const struct sockaddr *p_addr) noexcept {