Fix returned tc and hoplimit values for route with IPv6 encapsulation

For a route with IPv6 encapsulation, the traffic class and hop limit
values are interchanged when returned to userspace by the kernel.
For example, see below.

># ip route add 192.168.0.1 dev eth0.2 encap ip6 dst 0x50 tc 0x50 hoplimit 100 table 1000
># ip route show table 1000
192.168.0.1  encap ip6 id 0 src :: dst fe83::1 hoplimit 80 tc 100 dev eth0.2  scope link

Signed-off-by: Quentin Armitage <quentin@armitage.org.uk>
Signed-off-by: David S. Miller <davem@davemloft.net>