Upon receipt of the NETDEV_REGISTER event from the netdev notifier chain,
the IB stack registration is spawned off to a workqueue since that also
requires an rtnl lock.
There could be 2 kinds of races between the NETDEV_REGISTER and the
NETDEV_UNREGISTER event handling.
a)The NETDEV_UNREGISTER event is received in rapid succession after
the NETDEV_REGISTER event even before the work queue got a chance to run.
b)The NETDEV_UNREGISTER event is received while the workqueue that handles
registration with the IB stack is still in progress.

Handle both the races with a bit flag that is set just before the work item
is queued and cleared in the workqueue after the event is handled just
before the workqueue item is freed.

While adding the new flag, it was noted that the flags are all used in
*_bit() operations which expect a bit number and not a literal constant
with a bit set.  So change the numbers to be bit numbers.
Signed-off-by: Somnath Kotur <somnath.kotur@broadcom.com>
Signed-off-by: Doug Ledford <dledford@redhat.com>