In general, gall bladder polyps are benign and do not cause any problems. In your case, since you are getting an umbilical hernia fixed laproscopically, your doctor can remove the gall bladder at the same time, without much additional morbidity.
I would suggest you go ahead and get the gall bladder out since the long-term outcome of polyps (i.e., do they become malignant) is not entirely clear.