[SCSI] iscsi_transport: add support for net settings

Allows user space (iscsiadm) to send down network configuration
parameters for LLD to set private network configuration on the iSCSI
adapters.

Based on patch from Lalit Chandivade.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: James Bottomley <JBottomley@Parallels.com>