DNS: fix display of A6 address suffix field

Bug: 10652
Change-Id: Ibd119177feecd27d0c6baba255e7e3da37b131bd
Reviewed-on: https://code.wireshark.org/review/5043
Tested-by: Pascal Quantin <pascal.quantin@gmail.com>
Petri-Dish: Pascal Quantin <pascal.quantin@gmail.com>
Tested-by: Petri Dish Buildbot <buildbot-no-reply@wireshark.org>
Reviewed-by: Pascal Quantin <pascal.quantin@gmail.com>