BUG/MINOR: proxy: fix header_unique_id leak on deinit()

proxy header_unique_id wasn't cleaned up in proxy_free_defaults(),
resulting in small memory leak if "unique-id-header" was used on a
default proxy section.

It may be backported to all stable versions.

(cherry picked from commit 847c406)
Signed-off-by: Christopher Faulet <[email protected]>

Author: Darlelet

src/proxy.c

@@ -1458,6 +1458,7 @@ void proxy_free_defaults(struct proxy *defproxy)
 #if defined(CONFIG_HAP_TRANSPARENT)
 	ha_free(&defproxy->conn_src.bind_hdr_name);
 #endif
+	istfree(&defproxy->header_unique_id);
 	istfree(&defproxy->server_id_hdr_name);
 
 	http_ext_clean(defproxy);