i40e: Check client is open before calling client ops

We were having a race between the completion of the client open and
calls to the client ops so don't call a client op unless we are sure the
client is open.

Testing Hints: Load IWARP driver and make sure it works as expected.

Change-Id: I741f4f2aa4fcbfdad3e40dabbbb1b005856c396b
Signed-off-by: Catherine Sullivan <catherine.sullivan@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>