add  OFPXMT_OFB_METADATA into match of packet-in

1.3.2
The OXM TLVs must include context fields, that is, fields whose values cannot be determined from
the packet data. The standard context fields are OFPXMT_OFB_IN_PORT, OFPXMT_OFB_IN_PHY_PORT,
OFPXMT_OFB_METADATA and OFPXMT_OFB_TUNNEL_ID. Fields whose values are all-bits-zero should be
omitted.