IB/srp: Use block layer tags

Since the block layer already contains functionality to assign
a tag to each request, use that functionality instead of
reimplementing that functionality in the SRP initiator driver.
This change makes the free_reqs list superfluous. Hence remove
that list.

[hch: updated to use .use_blk_tags instead scsi_activate_tcq]
Signed-off-by: Bart Van Assche <bvanassche@acm.org>
Reviewed-by: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Christoph Hellwig <hch@lst.de>

drivers/infiniband/ulp/srp/ib_srp.h

@@ -116,7 +116,6 @@ struct srp_host {
 };
 
 struct srp_request {
-	struct list_head	list;
 	struct scsi_cmnd       *scmnd;
 	struct srp_iu	       *cmd;
 	union {
@@ -127,7 +126,6 @@ struct srp_request {
 	struct srp_direct_buf  *indirect_desc;
 	dma_addr_t		indirect_dma_addr;
 	short			nmdesc;
-	short			index;
 };
 
 /**
@@ -137,7 +135,6 @@ struct srp_request {
 struct srp_rdma_ch {
 	/* These are RW in the hot path, and commonly used together */
 	struct list_head	free_tx;
-	struct list_head	free_reqs;
 	spinlock_t		lock;
 	s32			req_lim;