[IPv4] SNMP: Refer correct memory location to display ICMP out-going statistics

While displaying ICMP out-going statistics as Out<name> counters in
/proc/net/snmp, the memory location for ICMP in-coming statistics
was referred by mistake.

Signed-off-by: Mitsuru Chinen <mitch@linux.vnet.ibm.com>
Acked-by: David L Stevens <dlstevens@us.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>