Add simple XMPP StartTLS analyzer.

This is a very simple XMPP analyzer that basically only can parse the
protocol until the client and server start negotiating a TLS session. At
that point, the TLS analyzer is attached.

While the basic case seems to be working, I fully expect that I missed
something and that this might break in a lot of cases.

scripts/base/protocols/xmpp/main.bro

@@ -0,0 +1,11 @@
+
+module XMPP;
+
+const ports = { 5222/tcp, 5269/tcp };
+redef likely_server_ports += { ports };
+
+event bro_init() &priority=5
+	{
+	Analyzer::register_for_ports(Analyzer::ANALYZER_XMPP, ports);
+	}
+