wireshark: Introduce and use vir_val_to_str()

wireshark: Introduce and use vir_val_to_str()

Wireshark offers val_to_str() function which converts numeric
value to string by looking up value ('val') in an array ('vs') of
<val, string> pairs. If no corresponding string is found, then
the value is formatted using given 'fmt' string.

Starting from wireshark-4.6.0 not only this function gained
another argument but also returns a strdup()-ed string. To keep
our code simple, let's introduce a wrapper so which can be then
adjusted as needed.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Peter Krempa <pkrempa@redhat.com>