qeth: check for completion of a running recovery

When a recovery is started for a qeth device, additional invocations
to change a mac address, to configure a VLAN interface on top, or to
add multicast addresses should wait till recovery is finished,
otherwise recovery might fail.

Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Signed-off-by: Frank Blaschka <frank.blaschka@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>