scsi: qla2xxx: Serialize session free in qlt_free_session_done

scsi: qla2xxx: Serialize session free in qlt_free_session_done

BugLink: http://bugs.launchpad.net/bugs/1770003
Add free_pending flag to serialize queueing of
free_work element onto the work queue

Signed-off-by: Quinn Tran <quinn.tran@cavium.com>
Signed-off-by: Himanshu Madhani <himanshu.madhani@cavium.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
(cherry picked from 1ae634eb28533b82f9777a47c1ade44cb8c0182b)
Signed-off-by: Gustavo Walbon <gwalbon@linux.vnet.ibm.com>
Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Sacilotto de Souza <kleber.souza@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>