The simplest way to explain the licensing is this: the LEM will identify a node and consume a license for each unique IP from which it receives logs. The Agent is smart enough to work with the manager if an IP changes because of DHCP, but if the same agent sends traffic over multiple unique IPs, that consumes multiple licenses.
If you can assign an affinity for the data to always use one interface, your server with two interfaces will only use one license.
There is some discussion on how to try and alleviate the accidental duplication of nodes, so that may become a non-issue in the future.