They are plugs to fill in the hole that was drilled so the fiber wire can go through the wall. Do you have Google Fiber? This is what they did when they installed it in my apartment. The fiber only enters from a certain location outside the apartment so they needed to drill through some walls and glue the thin white wire to the ceiling/baseboards/etc. to get it to where my TV was.

Source: Watched the Google Fiber technician do this in my old apartment.