backports: backport APIs for manipulating skb page fragments

backports: backport APIs for manipulating skb page fragments

This backports the APIs for manipulating skb page fragments
introduced by Ian via commit 131ea6675c on v3.2. Use the
LINUX_BACKPORT() namespace to avoid clashes with similar ports.
We skip skb_frag_dma_map() as that was already backported.
We also don't backport skb_frag_page() as that was already
backported before.

Since the skb fragment page was moved into its own struct as
part of the fragment our backport ends up using the old access
mechanisms for the framgement page. For details see a8605c6063.

mcgrof@ergon ~/linux-next (git::master)$ git describe --contains 131ea6675c
v3.2-rc1~129^2~421

mcgrof@ergon ~/linux-next (git::master)$ git describe --contains a8605c6063
v3.2-rc1~182^2~29

commit 131ea6675c761f655d43b808dd0fe83d15d5cdd3
Author: Ian Campbell <Ian.Campbell@citrix.com>
Date:   Fri Aug 19 06:25:00 2011 +0000

    net: add APIs for manipulating skb page fragments.

    The primary aim is to add skb_frag_(ref|unref) in order to remove the use of
    bare get/put_page on SKB pages fragments and to isolate users from subsequent
    changes to the skb_frag_t data structure.

    Signed-off-by: Ian Campbell <ian.campbell@citrix.com>
    Cc: "David S. Miller" <davem@davemloft.net>
    Cc: Eric Dumazet <eric.dumazet@gmail.com>
    Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
    Cc: netdev@vger.kernel.org
    Signed-off-by: David S. Miller <davem@davemloft.net>
Cc: Ian Campbell <ian.campbell@citrix.com>
Signed-off-by: Luis R. Rodriguez <mcgrof@do-not-panic.com>