MINOR: lua: add AppletTCP class and service

This class is used by Lua code for running as an applet called in TCP mode.
It defines also the lua service.
diff --git a/include/types/applet.h b/include/types/applet.h
index 21978bf..2254b0a 100644
--- a/include/types/applet.h
+++ b/include/types/applet.h
@@ -116,6 +116,11 @@
 			struct list wake_on_write;
 		} hlua;
 		struct {
+			struct hlua hlua;
+			int flags;
+			struct task *task;
+		} hlua_apptcp;
+		struct {
 			struct dns_resolvers *ptr;
 		} resolvers;
 		struct {