icmp: allow zero value for ICMP limits

Zero means limit is disabled, so the value doesn't need to be checked
against jitter value.

Fixes: ac44739fd834f51cacb26485a4140fd482e20150
Fixes: a03aff88a14448c3084a0384082ec996d7213897
(cherry picked from commit 4399e055ea610cdefa1470ad1ee614dd81ba5e56)