net: Fix vti use case with oif in dst lookups for IPv6

net: Fix vti use case with oif in dst lookups for IPv6

It occurred to me yesterday that a92a1e0451710 ("net: ipv6: Add
RT6_LOOKUP_F_IFACE flag if oif is set") means that xfrm6_dst_lookup
needs the FLOWI_FLAG_SKIP_NH_OIF flag set. This latest commit causes
the oif to be considered in lookups which is known to break vti. This
explains why 91c754603a34 did not the IPv6 change at the time it was
submitted.

Fixes: c2aa866fb2cf ("xfrm: Add oif to dst lookups")
Signed-off-by: David Ahern <dsa@cumulusnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>