Offset type of the packet.
start Offset from the start of the packet
mpls Offset from the head of MPLS
l2 Offset from the head of the L2 frame
l4 Offset from the head of L4 packet
l5 Offset from the head of the L5 packet
ipv4 Offset from the head of the IPv4 packet
ipv6 Offset from the head of the IPv6 packet