Split common functions like ioctl to export them.
This is a preparation to support to configure IPv6-over-IPv6 tunnel.
This patch also includes minor improvemen:
 o to stop to include unused headers
 o to change function static if it is not needed to be exported
Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: Stephen Hemminger <shemminger@osdl.org>