[CLEANUP] tcp: move some non tcp-specific layer6 processing out of proto_tcp

Some functions which act on generic buffer contents without being
tcp-specific were historically in proto_tcp.c. This concerns ACLs
and RDP cookies. Those have been moved away to more appropriate
locations. Ideally we should create some new files for each layer6
protocol parser. Let's do that later.
diff --git a/include/proto/acl.h b/include/proto/acl.h
index 488d75a..c35cee9 100644
--- a/include/proto/acl.h
+++ b/include/proto/acl.h
@@ -173,6 +173,10 @@
 /* always return false */
 int acl_match_nothing(struct acl_test *test, struct acl_pattern *pattern);
 
+/* Fetch the RDP cookie identified in the expression. */
+int acl_fetch_rdp_cookie(struct proxy *px, struct session *l4, void *l7, int dir,
+                         struct acl_expr *expr, struct acl_test *test);
+
 /* Checks that the pattern matches the end of the tested string. */
 int acl_match_end(struct acl_test *test, struct acl_pattern *pattern);