team: do RCU update path fixups

Use rcu_access_pointer and rcu_dereference_protected
to access RCU pointer by updater.
Use RCU_INIT_POINTER for NULL assignment of RCU pointer.

Signed-off-by: Jiri Pirko <jpirko@redhat.com>
Acked-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>