netfilter: ip6t_rpfilter: Fix regression with VRF interfaces

netfilter: ip6t_rpfilter: Fix regression with VRF interfaces

[ Upstream commit efb056e5f1f0036179b2f92c1c15f5ea7a891d70 ]

When calling ip6_route_lookup() for the packet arriving on the VRF
interface, the result is always the real (slave) interface. Expect this
when validating the result.

Fixes: acc641ab95b66 ("netfilter: rpfilter/fib: Populate flowic_l3mdev field")
Signed-off-by: Phil Sutter <phil@nwl.cc>
Signed-off-by: Pablo Neira Ayuso <pablo@netfilter.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>