My vote goes for LLB firstly because after LLB you will have a professional degree 2ndly if you got admitted in any good law college it would be life time experience i will suggest you Punjab University law college.
thirdly after LLB you can do you masters from US not only in Law but you will have option to opt Masters in criminal justice which again have scope.
fourthly Law is 200 marks subject in CSS so you can easily prepare for that.
n lastly it all depends what you have planned after Masters in IR? its important what goals you have set for future