tcp: out_of_order_queue do not use its lock

TCP out_of_order_queue lock is not used, as queue manipulation
happens with socket lock held and we therefore use the lockless
skb queue routines (as __skb_queue_head())

We can use __skb_queue_head_init() instead of skb_queue_head_init()
to make this more consistent.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>