bonding: reread information about speed and duplex when interface goes up

When an interface was enslaved when it was down, bonding thinks
it has speed -1 even after it goes up. This leads into selecting
a wrong active interface in active/backup mode on mixed 10G/1G or
1G/100M environment.

before:
 bonding: bond0: link status definitely up for interface eth5, 100 Mbps full duplex.
 bonding: bond0: link status definitely up for interface eth0, 100 Mbps full duplex.

after:
 bonding: bond0: link status definitely up for interface eth5, 10000 Mbps full duplex.
 bonding: bond0: link status definitely up for interface eth0, 1000 Mbps full duplex.

Signed-off-by: Krzysztof Piotr Oledzki <ole@ans.pl>
Signed-off-by: David S. Miller <davem@davemloft.net>