act_police: fix a crash during removal

The police action is using its own code to initialize tcf hash
info, which makes us to forgot to initialize a->hinfo correctly.
Fix this by calling the helper function tcf_hash_create() directly.

This patch fixed the following crash:

 BUG: unable to handle kernel NULL pointer dereference at 0000000000000028
 IP: [<ffffffff810c099f>] __lock_acquire+0xd3/0xf91
 PGD d3c34067 PUD d3e18067 PMD 0
 Oops: 0000 [#1] SMP
 CPU: 2 PID: 853 Comm: tc Not tainted 4.6.0+ #87
 Hardware name: Bochs Bochs, BIOS Bochs 01/01/2011
 task: ffff8800d3e28040 ti: ffff8800d3f6c000 task.ti: ffff8800d3f6c000
 RIP: 0010:[<ffffffff810c099f>]  [<ffffffff810c099f>] __lock_acquire+0xd3/0xf91
 RSP: 0000:ffff88011b203c80  EFLAGS: 00010002
 RAX: 0000000000000046 RBX: 0000000000000000 RCX: 0000000000000000
 RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000028
 RBP: ffff88011b203d40 R08: 0000000000000001 R09: 0000000000000000
 R10: ffff88011b203d58 R11: ffff88011b208000 R12: 0000000000000001
 R13: ffff8800d3e28040 R14: 0000000000000028 R15: 0000000000000000
 FS:  0000000000000000(0000) GS:ffff88011b200000(0000) knlGS:0000000000000000
 CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
 CR2: 0000000000000028 CR3: 00000000d4be1000 CR4: 00000000000006e0
 Stack:
  ffff8800d3e289c0 0000000000000046 000000001b203d60 ffffffff00000000
  0000000000000000 ffff880000000000 0000000000000000 ffffffff00000000
  ffffffff8187142c ffff88011b203ce8 ffff88011b203ce8 ffffffff8101dbfc
 Call Trace:
  <IRQ>
  [<ffffffff8187142c>] ? __tcf_hash_release+0x77/0xd1
  [<ffffffff8101dbfc>] ? native_sched_clock+0x1a/0x35
  [<ffffffff8101dbfc>] ? native_sched_clock+0x1a/0x35
  [<ffffffff810a9604>] ? sched_clock_local+0x11/0x78
  [<ffffffff810bf6a1>] ? mark_lock+0x24/0x201
  [<ffffffff810c1dbd>] lock_acquire+0x120/0x1b4
  [<ffffffff810c1dbd>] ? lock_acquire+0x120/0x1b4
  [<ffffffff8187142c>] ? __tcf_hash_release+0x77/0xd1
  [<ffffffff81aad89f>] _raw_spin_lock_bh+0x3c/0x72
  [<ffffffff8187142c>] ? __tcf_hash_release+0x77/0xd1
  [<ffffffff8187142c>] __tcf_hash_release+0x77/0xd1
  [<ffffffff81871a27>] tcf_action_destroy+0x49/0x7c
  [<ffffffff81870b1c>] tcf_exts_destroy+0x20/0x2d
  [<ffffffff8189273b>] u32_destroy_key+0x1b/0x4d
  [<ffffffff81892788>] u32_delete_key_freepf_rcu+0x1b/0x1d
  [<ffffffff810de3b8>] rcu_process_callbacks+0x610/0x82e
  [<ffffffff8189276d>] ? u32_destroy_key+0x4d/0x4d
  [<ffffffff81ab0bc1>] __do_softirq+0x191/0x3f4

Fixes: ddf97ccd ("net_sched: add network namespace support for tc actions")
Cc: Jamal Hadi Salim <jhs@mojatatu.com>
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>