vrf: do not push non-ND strict packets with a source LLA through packet taps again

Non-ND strict packets with a source LLA go through the packet taps
again, while non-ND strict packets with other source addresses do not,
and we can see a clone of those packets on the vrf interface (we should
not). This is due to a series of changes:

Commit 6f12fa77[1] made non-ND strict packets not being pushed again
in the packet taps. This changed with commit 205704c6[2] for those
packets having a source LLA, as they need a lookup with the orig_iif.

The issue now is those packets do not skip the 'vrf_ip6_rcv' function to
the end (as the ones without a source LLA) and go through the check to
call packet taps again. This check was changed by commit 6f12fa77[1]
and do not exclude non-strict packets anymore. Packets matching
'need_strict && !is_ndisc && is_ll_src' are now being sent through the
packet taps again. This can be seen by dumping packets on the vrf
interface.

Fix this by having the same code path for all non-ND strict packets and
selectively lookup with the orig_iif for those with a source LLA. This
has the effect to revert to the pre-205704c6[2] condition, which
should also be easier to maintain.

[1] 6f12fa77 ("vrf: mark skb for multicast or link-local as enslaved to VRF")
[2] 205704c6 ("vrf: packets with lladdr src needs dst at input with orig_iif when needs strict")

Fixes: 205704c6

 ("vrf: packets with lladdr src needs dst at input with orig_iif when needs strict")
Cc: Stephen Suryaputra <ssuryaextr@gmail.com>
Reported-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Antoine Tenart <atenart@kernel.org>
Reviewed-by: David Ahern <dsahern@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>