net: ipv6_stub: use ip6_dst_lookup_flow instead of ip6_dst_lookup

commit 6c8991f41546c3c472503dff1ea9daaddf9331c2 upstream.

ipv6_stub uses the ip6_dst_lookup function to allow other modules to
perform IPv6 lookups. However, this function skips the XFRM layer
entirely.

All users of ipv6_stub->ip6_dst_lookup use ip_route_output_flow (via the
ip_route_output_key and ip_route_output helpers) for their IPv4 lookups,
which calls xfrm_lookup_route(). This patch fixes this inconsistent
behavior by switching the stub to ip6_dst_lookup_flow, which also calls
xfrm_lookup_route().

This requires some changes in all the callers, as these two functions
take different arguments and have different return types.

Fixes: 5f81bd2e ("ipv6: export a stub for IPv6 symbols used by vxlan")
Reported-by: Xiumei Mu <xmu@redhat.com>
Signed-off-by: Sabrina Dubroca <sd@queasysnail.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
[bwh: Backported to 4.9:
 - Drop changes in lwt_bpf.c and mlx5
 - Initialise "dst" in drivers/infiniband/core/addr.c:addr_resolve()
   to avoid introducing a spurious "may be used uninitialised" warning
 - Adjust filename, context, indentation]
Signed-off-by: Ben Hutchings <ben.hutchings@codethink.co.uk>
Signed-off-by: Sasha Levin <sashal@kernel.org>