vxlan: fill ttl inherit info

When add vxlan ttl inherit support, I forgot to fill it when dump
vlxan info. Fix it now.

Fixes: 72f6d71e ("vxlan: add ttl inherit support")
Signed-off-by: Hangbin Liu <liuhangbin@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>