bonding: Gratuitous ARP gets dropped when first slave added

When the first slave is added (such as during bootup) the first
gratuitous ARP gets dropped. We don't see this drop during a failover.
The packet gets dropped in qdisc (noop_enqueue).

The fix is to delay the sending of gratuitous ARPs till the bond dev's
carrier is present.

It can also be worked around by setting num_grat_arp to more than 1.

Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: David S. Miller <davem@davemloft.net>