iscsi: Resolve iscsi_proto.h naming conflicts with drivers/target/iscsi

This patch renames the following iscsi_proto.h structures to avoid
namespace issues with drivers/target/iscsi/iscsi_target_core.h:

*) struct iscsi_cmd -> struct iscsi_scsi_req
*) struct iscsi_cmd_rsp -> struct iscsi_scsi_rsp
*) struct iscsi_login -> struct iscsi_login_req

This patch includes useful ISCSI_FLAG_LOGIN_[CURRENT,NEXT]_STAGE*,
and ISCSI_FLAG_SNACK_TYPE_* definitions used by iscsi_target_mod, and
fixes the incorrect definition of struct iscsi_snack to following
RFC-3720 Section 10.16. SNACK Request.

Also, this patch updates libiscsi, iSER, be2iscsi, and bn2xi to
use the updated structure definitions in a handful of locations.

Signed-off-by: Mike Christie <michaelc@cs.wisc.edu>
Signed-off-by: Nicholas A. Bellinger <nab@linux-iscsi.org>
diff --git a/drivers/scsi/libiscsi.c b/drivers/scsi/libiscsi.c
index 0c550d5..c552cd7 100644
--- a/drivers/scsi/libiscsi.c
+++ b/drivers/scsi/libiscsi.c
@@ -360,7 +360,7 @@
 	struct iscsi_conn *conn = task->conn;
 	struct iscsi_session *session = conn->session;
 	struct scsi_cmnd *sc = task->sc;
-	struct iscsi_cmd *hdr;
+	struct iscsi_scsi_req *hdr;
 	unsigned hdrlength, cmd_len;
 	itt_t itt;
 	int rc;
@@ -374,7 +374,7 @@
 		if (rc)
 			return rc;
 	}
-	hdr = (struct iscsi_cmd *) task->hdr;
+	hdr = (struct iscsi_scsi_req *)task->hdr;
 	itt = hdr->itt;
 	memset(hdr, 0, sizeof(*hdr));
 
@@ -830,7 +830,7 @@
 			       struct iscsi_task *task, char *data,
 			       int datalen)
 {
-	struct iscsi_cmd_rsp *rhdr = (struct iscsi_cmd_rsp *)hdr;
+	struct iscsi_scsi_rsp *rhdr = (struct iscsi_scsi_rsp *)hdr;
 	struct iscsi_session *session = conn->session;
 	struct scsi_cmnd *sc = task->sc;