[IPV6]: Seperate sit driver to extra module (addrconf.c changes)

This patch contains the changes to net/ipv6/addrconf.c to remove sit
specific code if the sit driver is not selected.

Signed-off-by: Joerg Roedel <joro-lkml@zlug.org>
Signed-off-by: YOSHIFUJI Hideaki <yoshfuji@linux-ipv6.org>
Signed-off-by: David S. Miller <davem@davemloft.net>