Setting up a meta match causes a kernel OOPS because of uninitialized
elements in tree.

[   37.322381] BUG: unable to handle kernel NULL pointer dereference at 0000000000000000
[   37.322381] IP: [<ffffffff883fc717>] :em_meta:em_meta_destroy+0x17/0x80

[   37.322381] Call Trace:
[   37.322381]  [<ffffffff803ec83d>] tcf_em_tree_destroy+0x2d/0xa0
[   37.322381]  [<ffffffff803ecc8c>] tcf_em_tree_validate+0x2dc/0x4a0
[   37.322381]  [<ffffffff803f06d2>] nla_parse+0x92/0xe0
[   37.322381]  [<ffffffff883f9672>] :cls_basic:basic_change+0x202/0x3c0
[   37.322381]  [<ffffffff802a3917>] kmem_cache_alloc+0x67/0xa0
[   37.322381]  [<ffffffff803ea221>] tc_ctl_tfilter+0x3b1/0x580
[   37.322381]  [<ffffffff803dffd0>] rtnetlink_rcv_msg+0x0/0x260
[   37.322381]  [<ffffffff803ee944>] netlink_rcv_skb+0x74/0xa0
[   37.322381]  [<ffffffff803dffc8>] rtnetlink_rcv+0x18/0x20
[   37.322381]  [<ffffffff803ee6c3>] netlink_unicast+0x263/0x290
[   37.322381]  [<ffffffff803cf276>] __alloc_skb+0x96/0x160
[   37.322381]  [<ffffffff803ef014>] netlink_sendmsg+0x274/0x340
[   37.322381]  [<ffffffff803c7c3b>] sock_sendmsg+0x12b/0x140
[   37.322381]  [<ffffffff8024de90>] autoremove_wake_function+0x0/0x30
[   37.322381]  [<ffffffff8024de90>] autoremove_wake_function+0x0/0x30
[   37.322381]  [<ffffffff803c7c3b>] sock_sendmsg+0x12b/0x140
[   37.322381]  [<ffffffff80288611>] zone_statistics+0xb1/0xc0
[   37.322381]  [<ffffffff803c7e5e>] sys_sendmsg+0x20e/0x360
[   37.322381]  [<ffffffff803c7411>] sockfd_lookup_light+0x41/0x80
[   37.322381]  [<ffffffff8028d04b>] handle_mm_fault+0x3eb/0x7f0
[   37.322381]  [<ffffffff8020c2fb>] system_call_after_swapgs+0x7b/0x80
Signed-off-by: Stephen Hemminger <shemminger@vyatta.com>
Signed-off-by: David S. Miller <davem@davemloft.net>