How to get rid of network broadcasting of port 17500
You can't "get rid of" these so easily. You're seeing this because other customers of your VPS provider are running Dropbox LAN sync.
Personally I just drop traffic from other nodes in the same subnet without bothering to log it. For example, if your VPS's IP address is 203.0.113.148 and prefix 24:
-A INPUT -s 203.0.113.0/24 ! -d 203.0.113.148 -m comment --comment "Noisy neighbors" -j DROP