net: openvswitch: silence suspicious RCU usage warning

ovs_flow_tbl_destroy always is called from RCU callback
or error path. It is no need to check if rcu_read_lock
or lockdep_ovsl_is_held was held.

ovs_dp_cmd_fill_info always is called with ovs_mutex,
So use the rcu_dereference_ovsl instead of rcu_dereference
in ovs_flow_tbl_masks_cache_size.

Fixes: 9bf24f59 ("net: openvswitch: make masks cache size configurable")
Cc: Eelco Chaudron <echaudro@redhat.com>
Reported-by:  <syzbot+c0eb9e7cdde04e4eb4be@syzkaller.appspotmail.com>
Reported-by:  <syzbot+f612c02823acb02ff9bc@syzkaller.appspotmail.com>
Signed-off-by: Tonghao Zhang <xiangxia.m.yue@gmail.com>
Acked-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>