vxlan: use a more suitable function when assigning NULL

vxlan: use a more suitable function when assigning NULL

When stopping the vxlan interface we detach it from the socket.
Use RCU_INIT_POINTER() and not rcu_assign_pointer() to do so.

Orabug: 29927196

Suggested-by: Stephen Hemminger <stephen@networkplumber.org>
Signed-off-by: Mark Bloch <markb@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
(cherry picked from commit 57d88182ea3e8763111882671fd7462289272f64)
Reviewed-by: Rama Nichanamatlu <rama.nichanamatlu@oracle.com>
Signed-off-by: Venkat Venkatsubra <venkat.x.venkatsubra@oracle.com>
Signed-off-by: Brian Maly <brian.maly@oracle.com>