It looks like Fannie Mae has at least one more big subprime-MBS related legal settlement coming its way. The Times has reported that the Royal Bank of Scotland could have to pay as much as £5 billion ($7.7 billion) to settle charges against it for selling toxic mortgage-backed securities to Fannie Mae / Federal National Mortgage Assctn Fnni Me (OTCBB:FNMA) and Freddie Mac / Federal Home Loan Mortgage Corp (OTCBB:FMCC) between 2005 and 2007, citing an unnamed source familiar with the negotiations (h/t Richard Partington at Bloomberg). Neither RBS nor the Federal Housing Finance Agency has commented on the report, but…