iscsi-target: kstrtou* configfs attribute parameter cleanups

This patch includes the conversion of iscsi-target configfs
attributes for NetworkPortal, NodeACL, TPG, IQN and Discovery
groups to use kstrtou*() instead of simple_strtou*().

It also cleans up new-line usage during iscsi_tpg_param_store_##name
to use isspace().

Signed-off-by: Joern Engel <joern@logfs.org>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>