Limiting closed port RST response from 266 to 200 packets/second.

Kernel default setting for icmp response is set to 200.
net.inet.icmp.icmplim sysctl limits.

Possible reasons are,
1. This generally means the system is being portscanned or a similar activity on the machine. In worst case someone trying to do DOS attack.
I suggest that you set the following sysctl variables,
net.inet.tcp.blackhole=2
net.inet.udp.blackhole=1

2. But it can also mean that a often-used service on the machine (like http or a database server) is down and you're getting a lot of failed connection requests from clients.