file: /proc/sys/net/ipv4/icmp_ratelimit
variable: net.ipv4.icmp_ratelimit
Official reference

Limit the maximal rates for sending ICMP packets whose type matches icmp_ratemask (see below) to specific targets. 0 to disable any limiting, otherwise the minimal space between responses in milliseconds. Note that another sysctl, icmp_msgs_per_sec limits the number of ICMP packets sent on all targets. Default: 1000