net: fix /proc/net/snmp as memory corruptor

icmpmsg_put() can happily corrupt kernel memory, using a static
table and forgetting to reset an array index in a loop.

Remove the static array since its not safe without proper locking.

Signed-off-by: Alexey Dobriyan <adobriyan@gmail.com>
Signed-off-by: Eric Dumazet <dada1@cosmosbay.com>
Signed-off-by: David S. Miller <davem@davemloft.net>