userspace: Add support for NSH MD1 match fields

userspace: Add support for NSH MD1 match fields

This patch adds support for NSH packet header fields to the OVS
control plane and the userspace datapath. Initially we support the
fields of the NSH base header as defined in
https://www.ietf.org/id/draft-ietf-sfc-nsh-13.txt
and the fixed context headers specified for metadata format MD1.
The variable length MD2 format is parsed but the TLV context headers
are not yet available for matching.

The NSH fields are modelled as experimenter fields with the dedicated
experimenter class 0x005ad650 proposed for NSH in ONF. The following
fields are defined:

NXOXM code            ofctl name    Size      Comment
=====================================================================
NXOXM_NSH_FLAGS       nsh_flags       8       Bits 2-9 of 1st NSH word
(0x005ad650,1)
NXOXM_NSH_MDTYPE      nsh_mdtype      8       Bits 16-23
(0x005ad650,2)
NXOXM_NSH_NEXTPROTO   nsh_np          8       Bits 24-31
(0x005ad650,3)
NXOXM_NSH_SPI         nsh_spi         24      Bits 0-23 of 2nd NSH word
(0x005ad650,4)
NXOXM_NSH_SI          nsh_si          8       Bits 24-31
(0x005ad650,5)
NXOXM_NSH_C1          nsh_c1          32      Maskable, nsh_mdtype==1
(0x005ad650,6)
NXOXM_NSH_C2          nsh_c2          32      Maskable, nsh_mdtype==1
(0x005ad650,7)
NXOXM_NSH_C3          nsh_c3          32      Maskable, nsh_mdtype==1
(0x005ad650,8)
NXOXM_NSH_C4          nsh_c4          32      Maskable, nsh_mdtype==1
(0x005ad650,9)

Co-authored-by: Johnson Li <johnson.li@intel.com>
Signed-off-by: Yi Yang <yi.y.yang@intel.com>
Signed-off-by: Jan Scheurich <jan.scheurich@ericsson.com>
Signed-off-by: Ben Pfaff <blp@ovn.org>