nvmet-tcp: constify nvmet_tcp_ops

nvmet_tcp_ops is never modified and can be made const to allow the
compiler to put it in read-only memory, as done in other transports.

Before:
   text    data     bss     dec     hex filename
  16164     160      12   16336    3fd0 drivers/nvme/target/tcp.o

After:
   text    data     bss     dec     hex filename
  16277      64      12   16353    3fe1 drivers/nvme/target/tcp.o
Signed-off-by: Max Gurtovoy <maxg@mellanox.com>
Reviewed-by: Himanshu Madhani <himanshu.madhani@oracle.com>
Reviewed-by: Israel Rukshin <israelr@mellanox.com>
Acked-by: Sagi Grimberg <sagi@grimberg.me>
Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

drivers/nvme/target/tcp.c

@@ -153,7 +153,7 @@ static LIST_HEAD(nvmet_tcp_queue_list);
 static DEFINE_MUTEX(nvmet_tcp_queue_mutex);
 
 static struct workqueue_struct *nvmet_tcp_wq;
-static struct nvmet_fabrics_ops nvmet_tcp_ops;
+static const struct nvmet_fabrics_ops nvmet_tcp_ops;
 static void nvmet_tcp_free_cmd(struct nvmet_tcp_cmd *c);
 static void nvmet_tcp_finish_cmd(struct nvmet_tcp_cmd *cmd);
 
@@ -1747,7 +1747,7 @@ static void nvmet_tcp_disc_port_addr(struct nvmet_req *req,
 	}
 }
 
-static struct nvmet_fabrics_ops nvmet_tcp_ops = {
+static const struct nvmet_fabrics_ops nvmet_tcp_ops = {
 	.owner			= THIS_MODULE,
 	.type			= NVMF_TRTYPE_TCP,
 	.msdbd			= 1,