Add a tag name to hamlib_port_t.

Note: I also sent this [upstream](https://sourceforge.net/p/hamlib/code/merge-requests/2/) but there's another merge request there that has had no comments on it and has been open since February, so I'm sending my patch here too, in hopes that it at least doesn't get overlooked like [the other person's](https://sourceforge.net/p/hamlib/code/merge-requests/1/) seems to have.

I am making a Haskell binding to hamlib and this anonymous struct was
creating some issues for me. I am not a C-coder by day, but I think this
is harmless to add here.

Signed-off-by: Ricky Elrod <ricky@elrod.me>