[PATCH] Add ipv6 support to rtl_tcp

I've prepared this patch in response to Debian bug #870804 https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=870804

It passes the text from the -a and -p options through getaddrinfo() and uses the first result that has a valid socket with a successful bind.

While not a complete bind to all possible valid names, it does appear to address the use case of the bug submitter without completely changing the program flow.

I submit this for inclusion in the osmocom rtl-sdr repo as it may be of use to others.

Thanks for your consideration, -Maitland