sit: fix an oops when IFLA_IPTUN_PROTO is not set
sit: fix an oops when IFLA_IPTUN_PROTO is not set

The use of this attribute has been added in 32b8a8e59c9c (sit: add IPv4 over
IPv4 support). It is optional, by default proto is IPPROTO_IPV6.

Signed-off-by: Nicolas Dichtel <7864bb1e0e12322ea18ea731d051b95b75140567@6wind.com>
Signed-off-by: David S. Miller <fe08d3c717adf2ae63592e4c9aec6e3e404d8e3e@davemloft.net>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs