Fnic: Fnic Driver crashed with NULL pointer reference

When issuing I/O request, if the I/O completes before returning from
fnic_queuecommand(), we may be referencing scsi_cmnd structure that may
be freed by interrupt handler. Acquring IO lock would synchronize
fnic_queuecommand and interrupt handler.

- Increment fnic version from 1.6.0.15 to 1.6.0.16

Signed-off-by: Hiral Shah <hishah@cisco.com>
Signed-off-by: Sesidhar Baddela <sebaddel@cisco.com>
Signed-off-by: Anil Chintalapati <achintal@cisco.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>