Nationstar Mortgage (NSM) shares soared about 17% early Monday after it said it will pay about $1.3 billion to buy some $215 billion in mortgage servicing assets from Bank of America (BAC). Nationstar was chief among a group of independent mortgage companies that moved into the residential mortgage market during the downturn, buying assets being shed by giants like BofA. About 47% of the portfolio consists of government-backed loans owned or