What were the "sons of God" in Genesis 6, according to Mormons?

This is similar to this and this other question about the subject, but here I am interested in the LDS church point of view. It's about this passage in Genesis 6:2 (here according to KJV ): > That the sons of God saw the daughters of men that they were fair; and > they took them wives of all which they chose. Note that above is the same text as the Genesis 6:2 in the KJV here at lds.org . According to one interpretation that I have read is that the "sons of God" were spirit beings who materialized (similar to the ones who visited Abraham in Genesis 18, and Lot in Genesis 19). Another one is that they were part of some group of humankind that married the daughters from the line of Cain. What is the Mormon interpretation on who these "sons of God" were?