cnic: Fix locking in init/exit calls.

cnic: Fix locking in init/exit calls.

The slow path ulp_init and ulp_exit calls to the bnx2i driver
are sleepable calls and therefore should not be protected using
rcu_read_lock.  Fix it by using mutex and refcount during these
calls.  cnic_unregister_driver() will now wait for the refcount
to go to zero before completing the call.

Signed-off-by: Michael Chan <[email protected]>
Reviewed-by: Benjamin Li <[email protected]>
Signed-off-by: David S. Miller <[email protected]>