net: Make criu do not fail on recent iproute2

Since iprule commit 67a990b81126 command "ip rule del" is not working anymore:

    iproute: disallow ip rule del without parameters

    Disallow run `ip rule del` without any parameter to avoid delete any first
    rule from table.

Signed-off-by: Andrey Jr. Melnikov <temnota.am@gmail.com>

So, criu restore fails with:

    Error (criu/net.c:1277): IP tool failed on rule delete

Fix that by explicit passing of rule's table.

v2: Use "ip rule flush" to main's and default's table rules at once.

travis-ci: success for net: Make criu do not fail on recent iproute2 (rev2)
Signed-off-by: Kirill Tkhai <ktkhai@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>