net: sched: act_bpf: remove dependency on rtnl lock

Use tcf spinlock to protect bpf action private data from concurrent
modification during dump and init. Remove rtnl lock assertion that is no
longer necessary.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>