tc_tests: break down _ICMP into more understandable bits

_ICMP used to be defined as just a long hex string and it was
difficult to remember what each byte stood for. With this change,
I made a breakdown with scapy, pasted it and broke down the hex
string into smaller significant pieces.

Change-Id: Ic6c5684ca8833807cf1dc05e9ccc4d97391c6168
Signed-off-by: Antoni S. Puimedon <asegurap@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/31171
Reviewed-by: Dan Kenigsberg <danken@redhat.com>