scsi: qla2xxx: Fix mailbox failure while deleting Queue pairs

In target mode driver, queue pairs are not created during driver load
time, instead they are created at the configuration time after chip
reset.  If a user tries to load/unload driver after queue pairs are
created, then there would be mailbox failure, while deleting queue
pairs.  Flag is added to check if queue pairs are created or not. Queue
pairs will be deleted only If they were created during target
configuration.

Signed-off-by: Sawan Chandak <sawan.chandak@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>