Cabbage has no special meaning. . . It's probably a nickname for you, probably changed from your name or appearance, and I don't think it should be derogatory.

For example, my classmates call me steamed bread. . . Can I eat?

If your classmates play Plants vs Zombies. . . There is an aggressive plant called Nepenthes cabbages. Personally, I think it's cute.

Generally speaking, don't worry, your classmates won't discriminate against you or anything. Personally, I think it's a compliment or a nickname ~