ip: add support of netconf messages

ip: add support of netconf messages

Example of the output:
$ ip monitor netconf&
[1] 24901
$ echo 0 > /proc/sys/net/ipv6/conf/all/forwarding
ipv6 dev lo forwarding off
ipv6 dev eth0 forwarding off
ipv6 all forwarding off
$ echo 1 > /proc/sys/net/ipv4/conf/eth0/forwarding
ipv4 dev eth0 forwarding on

$ ip -6 netconf
ipv6 all forwarding on mc_forwarding 0
$ ip netconf show dev eth0
ipv4 dev eth0 forwarding on rp_filter off mc_forwarding 1

Signed-off-by: Nicolas Dichtel <nicolas.dichtel@6wind.com>
Minor cleanup of original patch, made sure netconf.h matched
result of santized kernel headers