This is help from http://communities.vmware.com/docs/DOC-11775 I've created this code:
HostVMotionInfo vMotionInfo = hs.getConfig().getVmotion();
HostVirtualNicManager nicManager = hs.getHostVirtualNicManager();
nicManager.selectVnicForNicType("vmotion", (vMotionInfo.getNetConfig().getCandidateVnic()[0]).getDevice());