neigh: no need to call lookup_neigh_parms in neigh_parms_alloc

neigh_table.parms always exist and is initialized,kmemdup
can use it to create new neigh_parms, actually lookup_neigh_parms
here will return neigh_table.parms too.

Signed-off-by: Gao feng <gaofeng@cn.fujitsu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>