target: Convert se_tpg->acl_node_lock to ->acl_node_mutex

This patch converts se_tpg->acl_node_lock to struct mutex, so that
->acl_node_acl walkers in core_clear_lun_from_tpg() can block when
calling core_disable_device_list_for_node().

It also updates core_dev_add_lun() to hold ->acl_node_mutex when
calling core_tpg_add_node_to_devs() to build ->lun_entry_hlist
for dynamically generated se_node_acl.

Reviewed-by: Hannes Reinecke <hare@suse.de>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Sagi Grimberg <sagig@mellanox.com>
Signed-off-by: Nicholas Bellinger <nab@linux-iscsi.org>

include/target/target_core_base.h

@@ -876,7 +876,7 @@ struct se_portal_group {
 	/* Used for PR SPEC_I_PT=1 and REGISTER_AND_MOVE */
 	atomic_t		tpg_pr_ref_count;
 	/* Spinlock for adding/removing ACLed Nodes */
-	spinlock_t		acl_node_lock;
+	struct mutex		acl_node_mutex;
 	/* Spinlock for adding/removing sessions */
 	spinlock_t		session_lock;
 	struct mutex		tpg_lun_mutex;