Follow Stream: ensure linear performance with many packets

Follow Stream: ensure linear performance with many packets

Reverse the payload chunks list to achieve a running time of O(n) rather
than O(n²) for insertion of all chunks. Executing a RelWithDebInfo+ASAN
build with `tshark -r chargen-session.pcapng.gz -qz follow,tcp,hex,0`
previously took 11m5s to complete, but now finishes in 16 seconds.

Tested using a capture file with 152k TCP packets (from bug 11777).
Backport note: must update ui/gtk/follow_stream.c too.

Change-Id: Icf70d45f33d4399e53209fb6199d3809608c8d99
Reviewed-on: https://code.wireshark.org/review/28595
Petri-Dish: Peter Wu <peter@lekensteyn.nl>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>