datapath: Add basic MPLS support to kernel

Allow datapath to recognize and extract MPLS labels into flow keys
and execute actions which push, pop, and set labels on packets.

Based heavily on work by Leo Alterman.

Cc: Leo Alterman <lalterman@nicira.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.2
* Call skb_reset_mac_header() in skb_cb_set_mpls_stack()
  eth_hdr(skb) is non-NULL when called in skb_cb_set_mpls_stack().
* Add a call to skb_cb_set_mpls_stack() in ovs_packet_cmd_execute().
  I apologise that I have mislaid my notes on this but
  it avoids a kernel panic. I can investigate again if necessary.
* Use struct ovs_action_push_mpls instead of
  __be16 to decode OVS_ACTION_ATTR_PUSH_MPLS in validate_actions(). This is
  consistent with the data format for the attribute.
* Indentation fix in skb_cb_mpls_stack(). [cosmetic]

v2.1
* Manual rebase

Previous version(s) by Leo Alterman
user-space datapath: Add basic MPLS support to kernel

This is to match the kernel implementation in the
patch "datapath: Add basic MPLS support to kernel"
by Leo Alterman.

Cc: Leo Alterman <lalterman@nicira.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.2
* No change

v2.1
* Initial post
nx-match: Do not check pre-requisites for load actions

There are (or at least will be) cases where this check can produce false
positives.  For example, a flow which matches a non-MPLS packet and then
applies an MPLS push action followed by an action to load the MPLS label.

I believe this is the same problem that was recently discussed in
relation to set-field. In that case my understanding is that consensus
was to omit the check and potentially revisit the problem later.

Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.2
* No change

v2.1
* Initial post
User-Space MPLS actions and matches

This patch implements use-space datapath and non-datapath code
to match and use the datapath API set out in Leo Alterman's patch
"user-space datapath: Add basic MPLS support to kernel".

The resulting MPLS implementation supports:
* Pushing a single MPLS label
* Poping a single MPLS label
* Modifying an MPLS lable using set-field or load actions
  that act on the label value, tc and bos bit.
* There is no support for manipulating the TTL
  this is considered future work.

The single-level push pop limitation is implemented by processing
push, pop and set-field/load actions in order and discarding information
that would require multiple levels of push/pop to be supported.

e.g.
   push,push -> the first push is discarded
   pop,pop -> the first pop is discarded

This patch is based heavily on work by Ravi K.

Cc: Isaku Yamahata <yamahata@valinux.co.jp>
Cc: Ravi K <rkerur@gmail.com>
Signed-off-by: Simon Horman <horms@verge.net.au>

---

v2.2
* Manual Rebase

v2.1
* Reinstate user-space datapath changes
* Update to use datapath API set out in Leo Alterman's
  kernel datapath patch "datapath: Add basic MPLS support to kernel"
* Do not add:
  - OFPAT11_COPY_TTL_OUT/NXAST_COPY_TTL_OUT,
  - OFPAT11_COPY_TTL_IN/NXAST_COPY_TTL_IN.
  - OFPAT11_DEC_MPLS_TTL/NXAST_DEC_MPLS_TTL
  Add support for these later. Jesse Gross has commented that "It is envisaged
  this will be done "using set and some form of resubmit if necessary (as we do
  for IP)"
* Do not add:
  - OFPAT11_SET_MPLS_LABEL/NXAST_SET_MPLS_LABEL
  - OFPAT11_SET_MPLS_TC/NXAST_SET_MPLS_TC
  - OFPAT11_SET_MPLS_TTL/NXAST_SET_MPLS_TTL
  These may be handled by load/set-field actions.
* Remove inner_mpls_lse from struct flow
  - The new objective is to only support one layer of MPLS labels at this time
* Rearange action handling logic (again):
  - Logic to commit commit all MPLS actions is now in commit_mpls_action()
    which is called by commit_odp_actions().
  - Logic to compose push actions is in compose_mpls_push_action()
  - Logic to compose pop actions is in compose_mpls_pop_action()
  - There is no logic to compose mpls_set actions,
    compose_mpls_lse_action() has been removed.
  - This seems consistent with the handling of other actions.
* Correct mpls formatting in format_odp_action(),
  an error introduced by me.
* s/commit_mpls_/compose_mpls_/
  This seems to be more in keeping with the current naming convention.
* s/mpls_stack/mpls_bos/i
  This seems to be more in keeping with the wording in
  the OpenFlow 1.3 specification

v2.0
* Rebase to current master
  - First by Isaku Yamahata in July;
  - Then by me more recently.
* Remove datapath changes
  - This is intended to provide a first step for
    merging MPLS. The uers-space chagges seem
    largely uncontroversial while the datapath
    changes were incomplete with respect to
    agremment on the implementation for TTL actions
    and offloads.
* Correct dec_mpls_ttl to decerment ttl by 1 rather than 2
  - Fix by Isaku Yamahata
* Bug fixes to allow test suite to pass
* Make sparse clean
* Introduce encap_dl_type element to struct flow.
  This is used to store the dl_type of the encapsulated packet
  and is used by odp_flow_key_to_flow() and flow_compose() to
  allow eth_from_packet_or_flow() to be able to handle
  e.g. an MPLS encoded IPv4 packet.
* update packet.c:get_label_ttl_and_tc() to treat unknown eth type
  asn an error.
* Remove datapath changes

Previous Revisions by Ravi K