The Street – You may not know it but inside the U.K. Facebook (FB_) is in the online gambling business. Facebook added real money gambling a little over a year ago. Up until recently it was limited to bingo and online slots but now, through a partnership with Zynga (ZNGA_), Facebook users in the U.K. can play online poker for real money. None of the games are available in the U.S. yet. Legal hurdles including the Unlawful Internet Gambling Enforcement Act of 2006 have, until recently, kept almost all forms of online gambling outside of lottery ticket sales underground and…