backports: 6lowpan domain specific backport of inet_frag_lru_move()

backports: 6lowpan domain specific backport of inet_frag_lru_move()

We can't generalize a backport of inet_frag_lru_move() as
it requires modifying an internal struct netns_frags struct.
We work around this by extending the parent struct used within
6lowpan. We have two changes, one data structure change
and then a domain specific defines. Other subsystems which
require similar work can backport usage through similar
techniques.

The respective change upstream that put the lock on
struct netns_frags is commit 3ef0eb0db4 added by
through v3.9.

mcgrof@ergon ~/linux-next (git::master)$ git describe --contains 3ef0eb0db4
v3.9-rc1~139^2~232^2

commit 3ef0eb0db4bf92c6d2510fe5c4dc51852746f206
Author: Jesper Dangaard Brouer <brouer@redhat.com>
Date:   Mon Jan 28 23:45:51 2013 +0000

    net: frag, move LRU list maintenance outside of rwlock

    Updating the fragmentation queues LRU (Least-Recently-Used) list,
    required taking the hash writer lock.  However, the LRU list isn't
    tied to the hash at all, so we can use a separate lock for it.

    Original-idea-by: Florian Westphal <fw@strlen.de>
    Signed-off-by: Jesper Dangaard Brouer <brouer@redhat.com>
    Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Cc: Alexander Smirnov <alex.bluesman.smirnov@gmail.com>
Cc: Dmitry Eremin-Solenikov <dbaryshkov@gmail.com>
Cc: linux-zigbee-devel@lists.sourceforge.net
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>