There are some objects that are common in all the places
which are used to keep track of frag queues, they are:

 * hash table
 * LRU list
 * rw lock
 * rnd number for hash function
 * the number of queues
 * the amount of memory occupied by queues
 * secret timer

Move all this stuff into one structure (struct inet_frags)
to make it possible use them uniformly in the future. Like
with the previous patch this mostly consists of hunks like

-    write_lock(&ipfrag_lock);
+    write_lock(&ip4_frags.lock);

To address the issue with exporting the number of queues and
the amount of memory occupied by queues outside the .c file
they are declared in, I introduce a couple of helpers.
Signed-off-by: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>

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: NPavel Emelyanov <xemul@openvz.org>
Signed-off-by: NDavid S. Miller <davem@davemloft.net>