Dual link is one serializer connected to one deserializer with two links in between. In this mode in GMSL2, two links work together to deliver 12Gbps of total throughput from serializer to deserializer. Data is striped between the links, so the links are not independent.
For example, the MAX96751 can be operated in dual link mode with a MAX96752 to allow for 12Gbps of total throughput on the link.