net/sched: act_psample: Remove unnecessary ASSERT_RTNL

The ASSERT_RTNL is not necessary in the init function, as it does not
touch any rtnl protected structures, as opposed to the mirred action which
does have to hold a net device.

Reported-by: Cong Wang <xiyou.wangcong@gmail.com>
Reviewed-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: Yotam Gigi <yotamg@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>