Add worker-handoff node

Add worker-handoff node

worker-handoff node is universal node which taakes packets
from the input node and hands them over to worker threads.
Currently it supports flow hashing based on ipv4, ipv6 and
mpls headers.

New cli:

set interface handoff <intrerface-name> workers <list>

e.g.

set interface handoff TenGigabitEthernet2/0/0 workers 3-6,9-10

Change-Id: Iaf0df83e69bb0e84969865e0e1cdb000b0864cf5
Signed-off-by: Damjan Marion <[email protected]>