[IP] TUNNEL: Fix to be built with user application.

include/linux/if_tunnel.h is broken for user application
because it was changed to use __be32 which is required
to include linux/types.h in advance but didn't.

(This issue is found when building MIPL2 daemon. We are not sure this
is the last header to be fixed about __be32.)

Signed-off-by: Masahide NAKAMURA <nakam@linux-ipv6.org>
Signed-off-by: TAKAMIYA Noriaki <takamiya@po.ntts.co.jp>
Signed-off-by: David S. Miller <davem@davemloft.net>