sunrpc: Use rcu_barrier() on unload.

sunrpc: Use rcu_barrier() on unload.

The sunrpc module uses rcu_call() thus it should use rcu_barrier() on
module unload.

Have not verified that the possibility for new call_rcu() callbacks
has been disabled.  As a hint for checking, the functions calling
call_rcu() (unx_destroy_cred and generic_destroy_cred) are
registered as crdestroy function pointer in struct rpc_credops.

Acked-by: Paul E. McKenney <[email protected]>
Acked-by: Trond Myklebust <[email protected]>
Signed-off-by: Jesper Dangaard Brouer <[email protected]>
Signed-off-by: David S. Miller <[email protected]>