datapath: Set packet egress_tun_info.

datapath: Set packet egress_tun_info.

packet execute is setting egress_tun_info in skb->cb, rather
than packet->cb. skb is netlink msg skb. This causes corruption
in netlink skb state stored in skb->cb (NETLINK_CB) which
results in following deadlock in netlink code.

=============================================
[ INFO: possible recursive locking detected ]
3.2.62 #2
---------------------------------------------
handler55/22851 is trying to acquire lock:
 (genl_mutex){+.+.+.}, at: [<ffffffff81471ad7>] genl_lock+0x17/0x20

but task is already holding lock:
 (genl_mutex){+.+.+.}, at: [<ffffffff81471ad7>] genl_lock+0x17/0x20

other info that might help us debug this:
 Possible unsafe locking scenario:

       CPU0
       ----
  lock(genl_mutex);
  lock(genl_mutex);

 *** DEADLOCK ***

 May be due to missing lock nesting notation

1 lock held by handler55/22851:
 #0:  (genl_mutex){+.+.+.}, at: [<ffffffff81471ad7>] genl_lock+0x17/0x20

stack backtrace:
Pid: 22851, comm: handler55 Tainted: G           O 3.2.62 #2
Call Trace:
 [<ffffffff81097bb2>] print_deadlock_bug+0xf2/0x100
 [<ffffffff81099b99>] validate_chain+0x579/0x860
 [<ffffffff8109a17c>] __lock_acquire+0x2fc/0x4f0
 [<ffffffff8109aab0>] lock_acquire+0xa0/0x180
 [<ffffffff81519070>] __mutex_lock_common+0x60/0x420
 [<ffffffff8151959a>] mutex_lock_nested+0x4a/0x60
 [<ffffffff81471ad7>] genl_lock+0x17/0x20
 [<ffffffff81471af6>] genl_rcv+0x16/0x40
 [<ffffffff8146ff72>] netlink_unicast+0x2f2/0x310
 [<ffffffff81470159>] netlink_ack+0x109/0x1f0
 [<ffffffff8147030b>] netlink_rcv_skb+0xcb/0xd0
 [<ffffffff81471b05>] genl_rcv+0x25/0x40
 [<ffffffff8146ff72>] netlink_unicast+0x2f2/0x310
 [<ffffffff8147134c>] netlink_sendmsg+0x28c/0x3d0
 [<ffffffff8143375f>] sock_sendmsg+0xef/0x120
 [<ffffffff81435766>] ___sys_sendmsg+0x416/0x430
 [<ffffffff81435949>] __sys_sendmsg+0x49/0x90
 [<ffffffff814359a9>] sys_sendmsg+0x19/0x20
 [<ffffffff8152432b>] system_call_fastpath+0x16/0x1b

Reported-by: Joe Stringer <joestringer@nicira.com>
Signed-off-by: Pravin B Shelar <pshelar@nicira.com>
Acked-by: Joe Stringer <joestringer@nicira.com>