[IBAL] crash on IBBUS disabling while mad traffic. [mlnx: 4275]

[IBAL] crash on IBBUS disabling while mad traffic. [mlnx: 4275]

__ioc_query_sa takes references on IOC PnP service before sending the node and path_record requests.
But these references get released at the end of __node_rec_cb and __path_rec_cb, while __process_sweep routine, which performs the IOU sweeping, is just scheduled to run in an async thread.
If the test happens to unload the driver after __node_rec_cb and __path_rec_cb and before __process_sweep started to run, IOC PnP service gets released and __process_sweep crashes.

The patch takes a reference on IOC PnP service before scheduling a thread for __process_sweep and releases the reference at the end of __process_sweep.
(Pay attention, that __process_sweep schedules a thread for itself twice while moving through its FSM:
SWEEP_IOU_INFO --> SWEEP_IOC_PROFILE --> SWEEP_SVC_ENTRIES --> SWEEP_COMPLETE)

git-svn-id: svn://openib.tc.cornell.edu/gen1@2144 ad392aa1-c5ef-ae45-8dd8-e69d62a5ef86