Register timeout when using TCP

[phanmn]

Hi thank you for the awesome project!

I'm starting a sip registrar service in my Elixir project, it works fine with UDP but it returns timeout when trying with TCP!

{:error, {:exit, :timeout}}

Here is my simple project https://github.com/phanmn/ex-pbx

We can start with Iex and using this command to register with TCP

:nksip_uac.register(:client, "<sip:127.0.0.1;transport=tcp>", [{:sip_pass, "1234"}, :contact, {:get_meta, [<<"contact">>]}])

This is a command to register with UDP

:nksip_uac.register(:client, "sip:127.0.0.1", [{:sip_pass, "1234"}, :contact, {:get_meta, [<<"contact">>]}])

Please give me some hints, many thanks!