They will be created at output, if ever needed. This avoids creating
empty neighbor entries when TPROXYing/Forwarding packets for addresses
that are not even directly reachable.

Note that IPv4 already handles it this way. No neighbor entries are
created for local input.

Tested by myself and customer.
Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: Marcelo Ricardo Leitner <mleitner@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>