Use g_hash_table_new_full to free some values

Fixes a good 80-90KB of leaks in certain cases.

Bug: 10261
Change-Id: I81d57ac67219e730b03649b9fdfc2306807bdb97
Reviewed-on: https://code.wireshark.org/review/2879
Reviewed-by: Anders Broman <a.broman58@gmail.com>