"Don't like" is simply the negation of 'like'. If you don't like something, you don't have to hate it. "Dislike" is a verb that means the opposite of 'like'. If you dislike something, you hate it to at least some small degree. Most of the time "don't like" is used to mean 'dislike', but "don't like" also includes the possibility of neutrality. Ex: "I don't dislike maths" doesn't mean "I like maths", but rather "I either like maths or don't care about it". "I don't like or dislike maths" means you don't have any emotions towards maths, you are just neutral.

They are the same. Commonly, people use "I don't like".