ipv4: icmp: validate reply type before using icmp_pointers

In the Linux kernel, the following vulnerability has been resolved: ipv4: icmp: validate reply type before using icmp_pointers Extended echo replies use ICMP_EXT_ECHOREPLY as the outbound reply type. That value is outside the range covered by icmp_pointers[], which only describes the traditional ICMP types up to NR_ICMP_TYPES. Avoid consulting icmp_pointers[] for reply types outside that range, and use array_index_nospec() for the remaining in-range lookup. Normal ICMP replies keep their existing behavior unchanged.