Chhalla or Challa is such a common word in Punjabi poetry. Be it Challa India to aaya or Jab Tak Hai Jaan's Challa ki labhda phire. Challa is as such a simple thing, a ring.
However, this challa comes from the word, Jhalla, which is Hindi, used for someone who is mad, someone who's not orderly.
The meaning of Challa may vary across poetry, across compositions, however, mostly it means a young man, someone who's a little crazy, someone in love, or someone who just roams around freely.
For the Lyrics and English translation of the song challa from Jab Tak Hai Jaan, check THIS POST.
Check All Lyrics-Translations and Meanings from Jab Tak Hai Jaan HERE.