Several years back, there was a major thread here, on breast feeding. If my memory serves me right, it was about the inapropriate place, this woman was breastfeeding, in the main dining room, at the table. Added outrageous behavior, added to the issue. There was lots more, but you get the gist.
Even in this day and age, there are people who, are simply uncomfortable with the natural process of breastfeeding. My only advice would be to, take the time to feed the baby, in a private & calm environment.
You don't say what ship you are sailing..some ships don't have fridges. If so, just ask your room steward to remove all the goodies inside, so, you can have all the room you need.
I hope you enjoy the cruise, and, oh one more tip...bring a little blow up pool, to keep by your chair, at the pool for your baby to enjoy.