[IPV4] SNMP: Display new statistics at /proc/net/netstat

This displays the statistics specified in the updated IP-MIB RFC
(RFC4293) in /proc/net/netstat. The reason why these are not displayed
in /proc/net/snmp is that some existing utilities are developed under
the assumption which ipstat items in /proc/net/snmp is unchanged.

Signed-off-by: Mitsuru Chinen <mitch@linux.vnet.ibm.com>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>