docs: add Tobias' work into dissector section

Signed-off-by: Daniel Borkmann <dborkman@redhat.com>
stun: Use set_reuseaddr() instead of open-coding it

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>
xutils: Fix coding style issue in set_reuseaddr()

Signed-off-by: Tobias Klauser <tklauser@distanz.ch>