net_sched: act: clean up tca_action_flush()

We could allocate tc_action on stack in tca_action_flush(),
since it is not large.

Also, we could use create_a() in tcf_action_get_1().

Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Cc: David S. Miller <davem@davemloft.net>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: David S. Miller <davem@davemloft.net>