[SCSI] qla2xxx: do not reset dev_loss_tmo in slave callout

This fixes a bug where the driver was resetting the
rport dev_loss_tmo when devices were added by adding
support for the get_host_def_dev_loss_tmo callout.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <James.Bottomley@suse.de>