scsi: qla2xxx: Add support for minimum link speed

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