SAN FRANCISCO (Reuters) - As it prepares for one of the biggest IPOs ever, Facebook is coming under the same fierce attacks being waged against other big technology companies: patent lawsuits. Last year, Facebook was named as a defendant in 22 lawsuits accusing it of patent infringement, double the number from 2010, according to a Reuters analysis of court documents on legal database Westlaw, a Thomson Reuters unit. Among the lawsuits is one alleging Facebook violated a patent that covers the core ability to transmit messages to large networks of users. ...