This is good that you are so contious about your future plan.
In my opinion you should do prepration for GATE exam.Because in GATE paper, the whole syllabus is so perfectly desgined so that your all concept,from beginning to end, is automatically revised & if you work hard,little bit, then i am sure that you can crack it easily.
Look paper of GATE is not hard, it is totally concept based. Just think about that, time duration is about 3:00 hours,100 questions which include 1 & 2 marks questions, so you can imagine easily that problome is not so big & difficult. If your concept is clear then you can score easily. It is totally logic based or if you can't crack gate so don't worry, by this you are prepare for your interviews.But i suuggest, if you do M.Tech. from IITs/NITs & other reputed engg. colleges, then it is not necessary that, only teaching option is open. Most of the big IT companies offers higher salary as compare to B.Tech. graduate.
If you are not interested then you can do 3/6 months courses of advanced software such as mainframe,oracle etc.
yeah! C-dac is also a good option, you can choose it, but this is my personal suggestion for you dear, don't waste the time, just do prepare for GATE!
All The Best!