iscsi-target: Allow ->MaxXmitDataSegmentLength assignment for iser discovery

This patch changes iscsi_set_connection_parameters() to allow
conn_ops->MaxXmitDataSegmentLength assignement to occur during
in-band iser send-targets discovery, as this value is required
by TEXT response processing code.

Reported-by: Or Gerlitz <ogerlitz@mellanox.com>
Cc: Or Gerlitz <ogerlitz@mellanox.com>
Cc: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>