neigh: restore old behaviour of default parms values

neigh: restore old behaviour of default parms values

Previously inet devices were only constructed when addresses are added.
Therefore the default neigh parms values they get are the ones at the
time of these operations.

Now that we're creating inet devices earlier, this changes the behaviour
of default neigh parms values in an incompatible way (see bug #8519).

This patch creates a compromise by setting the default values at the
same point as before but only for those that have not been explicitly
set by the user since the inet device's creation.

Introduced by:
commit da6b8022120955a56dbf326e7a4b9097756b56ed
Author: Herbert Xu <herbert@gondor.apana.org.au>
Date:   Thu Feb 22 01:53:47 2007 +0900

    [IPV4] devinet: Register inetdev earlier.

Signed-off-by: Jiri Pirko <jiri@resnulli.us>
Signed-off-by: David S. Miller <davem@davemloft.net>