[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>
diff --git a/fs/ecryptfs/netlink.c b/fs/ecryptfs/netlink.c
index 8405d21..fe91863 100644
--- a/fs/ecryptfs/netlink.c
+++ b/fs/ecryptfs/netlink.c
@@ -229,7 +229,7 @@
 
 	ecryptfs_nl_sock = netlink_kernel_create(NETLINK_ECRYPTFS, 0,
 						 ecryptfs_receive_nl_message,
-						 THIS_MODULE);
+						 NULL, THIS_MODULE);
 	if (!ecryptfs_nl_sock) {
 		rc = -EIO;
 		ecryptfs_printk(KERN_ERR, "Failed to create netlink socket\n");