[INET]: Move common fields from frag_queues in one place.

Introduce the struct inet_frag_queue in include/net/inet_frag.h
file and place there all the common fields from three structs:

 * struct ipq in ipv4/ip_fragment.c
 * struct nf_ct_frag6_queue in nf_conntrack_reasm.c
 * struct frag_queue in ipv6/reassembly.c

After this, replace these fields on appropriate structures with
this structure instance and fix the users to use correct names
i.e. hunks like

-    atomic_dec(&fq->refcnt);
+    atomic_dec(&fq->q.refcnt);

(these occupy most of the patch)
Signed-off-by: Pavel Emelyanov <xemul@openvz.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

include/net/inet_frag.h

+#ifndef __NET_FRAG_H__
+#define __NET_FRAG_H__
+
+struct inet_frag_queue {
+	struct hlist_node	list;
+	struct list_head	lru_list;   /* lru list member */
+	spinlock_t		lock;
+	atomic_t		refcnt;
+	struct timer_list	timer;      /* when will this queue expire? */
+	struct sk_buff		*fragments; /* list of received fragments */
+	ktime_t			stamp;
+	int			len;        /* total length of orig datagram */
+	int			meat;
+	__u8			last_in;    /* first/last segment arrived? */
+
+#define COMPLETE		4
+#define FIRST_IN		2
+#define LAST_IN			1
+};
+
+#endif