test/ipsec: add reference packet to check decryption

Currently, only internal encryption and decryption were tested but the
implementation might not be the on it is supposed to be.

Add reference packets generated using Ubuntu-16.04, iproute2 and ping:
 # ip -V
 ip utility, iproute2-ss151103
 # uname -a
 Linux router-vm 4.4.0-62-generic #83-Ubuntu SMP Wed Jan 18 14:10:15 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
 # ping -V
 ping utility, iputils-s20160308

Signed-off-by: Thomas Faivre <thomas.faivre@6wind.com>