In rtnl_fdb_dump() when the fdb_dump ndo op is not populated
we never set the idx value so that cb->arg[0] is always 0.
Resulting in a endless loop of messages.
net: generic fdb support for drivers without ndo_fdb_<op>
CC: Vlad Yasevich <vyasevic@redhat.com> Signed-off-by: John Fastabend <john.r.fastabend@intel.com> Signed-off-by: David S. Miller <davem@davemloft.net>