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/src/session.c b/src/session.c
index 0c23364..d160a05 100644
--- a/src/session.c
+++ b/src/session.c
@@ -166,7 +166,7 @@
 	/* now evaluate the tcp-request layer4 rules. We only need a session
 	 * and no stream for these rules.
 	 */
-	if ((l->options & LI_O_TCP_RULES) && !tcp_exec_req_rules(sess)) {
+	if ((l->options & LI_O_TCP_L4_RULES) && !tcp_exec_l4_rules(sess)) {
 		/* let's do a no-linger now to close with a single RST. */
 		setsockopt(cfd, SOL_SOCKET, SO_LINGER, (struct linger *) &nolinger, sizeof(struct linger));
 		ret = 0; /* successful termination */