[SCSI] iscsi: rm channel usage from iscsi

I do not remember what I was thinking when we added the channel
as a argument to the session create function. It was probably
due to too much cut and paste work from the FC transport class.

The channel is meaningless for iscsi drivers so this patch drops
its usage everywhere in the iscsi related code.

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