[SCSI] qla2xxx: Allow an override of the registered maximum LUN.

The 'max_lun' value registered for each scsi_host is currently
capped at 0xffff.  The new module parameter can allow for
2nd-level flat-space addressing method-infrastructure to be
supported.

Signed-off-by: Andrew Vasquez <andrew.vasquez@qlogic.com>
Signed-off-by: Madhuranath Iyengar <Madhu.Iyengar@qlogic.com>
Signed-off-by: James Bottomley <jbottomley@parallels.com>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>