The Kajlas Ive come across are jats from Haryana (including me). I found a brief history about Kajla at
http://www.jatland.com/home/Kajla.
However, Hansraj Kajla, a well known spokesperson from California is not a Jat.(
http://www.friendsofsouthasia.org/textbook/FOSACACPressRelea... ).
A Bangladeshi friend of mine also told me of a Kajla river and a town by the same name in Bangladesh, (near Khulna) but as far as he knows, it is not a sir-name in Bengal/Bangladesh. (
http://www.multimap.com/wi/204156.htm )