Replace ip6_to_str and ip6_guint8_to_str with address_to_str and tvb_ip_to_str.

Change-Id: I1d258923a7a63539ec8456d3e306bca5016a1e4b
Reviewed-on: https://code.wireshark.org/review/6060
Petri-Dish: Michael Mann <mmann78@netscape.net>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>
Reviewed-by: Michael Mann <mmann78@netscape.net>