[IPV4]: Use kmemdup in net/ipv4/devinet.c

Code diff stats:

[acme@newtoy net-2.6.20]$ codiff /tmp/devinet.o.before /tmp/devinet.o.after
/pub/scm/linux/kernel/git/acme/net-2.6.20/net/ipv4/devinet.c:
  devinet_sysctl_register |  -38
 1 function changed, 38 bytes removed
[acme@newtoy net-2.6.20]$

Signed-off-by: Arnaldo Carvalho de Melo <acme@mandriva.com>