qla2xxx: Enable SLER conditionally in target mode.

Sequence level error recovery (aka FC Tape) is not really required
for disk devices. On heavily loaded system, with slow turn around,
a bunch of status enquiries using REC puts additional burden to the
target, so just turn off SLER by default.

Signed-off-by: Arun Easi <arun.easi@qlogic.com>
Signed-off-by: Saurav Kashyap <saurav.kashyap@qlogic.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>