bonding: start slaves with link down for ARP monitor

Initialize slave device link state as down if ARP monitor is
active and net_carrier_ok() returns zero. Also shift initial
value of its last_arp_tx so that it doesn't immediately cause
fake detection of "up" state.

When ARP monitoring is used, initializing the slave device with
up link state can cause ARP monitor to detect link failure
before the device is really up (with igb driver, this can take
more than two seconds).

Signed-off-by: Michal Kubecek <mkubecek@suse.cz>
Signed-off-by: Jay Vosburgh <fubar@us.ibm.com>
Signed-off-by: Flavio Leitner <fbl@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>