QUIC: fix Initial dissection (draft -13)

QUIC: fix Initial dissection (draft -13)

Recognize the Token field in the Initial Packet. Accept Initial Packet
from server and adjust connection tracking logic to take this into
account.

Tested with ngtcp2-13.pcap, now the Initial packets can be decrypted
(even if the containing frames are not correctly handled).

Change-Id: I5937fb85172a2f93d1b4a4ed7667474ec04f95fc
Ping-Bug: 13881
Reviewed-on: https://code.wireshark.org/review/29641
Petri-Dish: Alexis La Goutte <alexis.lagoutte@gmail.com>
Tested-by: Petri Dish Buildbot
Reviewed-by: Anders Broman <a.broman58@gmail.com>