ip_tunnel: fix setting ttl and tos value in collect_md mode

ttl and tos variables are declared and assigned, but are not used in
iptunnel_xmit() function.

Fixes: cfc7381b ("ip_tunnel: add collect_md mode to IPIP tunnel")
Cc: Alexei Starovoitov <ast@fb.com>
Signed-off-by: Haishuang Yan <yanhaishuang@cmss.chinamobile.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>