[NETLINK]: Switch cb_lock spinlock to mutex and allow to override it

Switch cb_lock to mutex and allow netlink kernel users to override it
with a subsystem specific mutex for consistent locking in dump callbacks.
All netlink_dump_start users have been audited not to rely on any
side-effects of the previously used spinlock.

Signed-off-by: Patrick McHardy <kaber@trash.net>
Signed-off-by: David S. Miller <davem@davemloft.net>

drivers/scsi/scsi_netlink.c

@@ -168,7 +168,8 @@ scsi_netlink_init(void)
 	}
 
 	scsi_nl_sock = netlink_kernel_create(NETLINK_SCSITRANSPORT,
-				SCSI_NL_GRP_CNT, scsi_nl_rcv, THIS_MODULE);
+				SCSI_NL_GRP_CNT, scsi_nl_rcv, NULL,
+				THIS_MODULE);
 	if (!scsi_nl_sock) {
 		printk(KERN_ERR "%s: register of recieve handler failed\n",
 				__FUNCTION__);