CLEANUP: tcp rules: mention everywhere that tcp-conn rules are L4

This is in order to make integration of tcp-request-session cleaner :
- tcp_exec_req_rules() was renamed tcp_exec_l4_rules()
- LI_O_TCP_RULES was renamed LI_O_TCP_L4_RULES
  (LI_O_*'s horrible indent was also fixed and a provision was left
   for L5 rules).
diff --git a/include/proto/proto_tcp.h b/include/proto/proto_tcp.h
index 8ca7290..05b6e02 100644
--- a/include/proto/proto_tcp.h
+++ b/include/proto/proto_tcp.h
@@ -38,7 +38,7 @@
 int tcp_drain(int fd);
 int tcp_inspect_request(struct stream *s, struct channel *req, int an_bit);
 int tcp_inspect_response(struct stream *s, struct channel *rep, int an_bit);
-int tcp_exec_req_rules(struct session *sess);
+int tcp_exec_l4_rules(struct session *sess);
 
 /* TCP keywords. */
 void tcp_req_conn_keywords_register(struct action_kw_list *kw_list);