ipip: fix a regression in ioctl

ipip: fix a regression in ioctl

This is a regression introduced by
commit 3b879fe658f251dfac5660 (IPIP: Use ip-tunneling code.)

Similar to GRE tunnel, previously we only check the parameters
for SIOCADDTUNNEL and SIOCCHGTUNNEL, after that commit, the
check is moved for all commands.

So, just check for SIOCADDTUNNEL and SIOCCHGTUNNEL.

Also, the check for i_key, o_key etc. is suspicious too,
which did not exist before, reset them before passing
to ip_tunnel_ioctl().

Cc: Pravin B Shelar <pshelar@nicira.com>
Cc: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Cong Wang <amwang@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>