ethdev: move egress metadata to dynamic field

ethdev: move egress metadata to dynamic field

The dynamic mbuf fields were introduced by [1]. The egress metadata is
good candidate to be moved from statically allocated field tx_metadata to
dynamic one. Because mbufs are used in half-duplex fashion only, it is
safe to share this dynamic field with ingress metadata.

The shared dynamic field contains either egress (if application going to
transmit mbuf with tx_burst) or ingress (if mbuf is received with rx_burst)
metadata and can be accessed by RTE_FLOW_DYNF_METADATA() macro or with
rte_flow_dynf_metadata_set() and rte_flow_dynf_metadata_get() helper
routines. PKT_TX_DYNF_METADATA/PKT_RX_DYNF_METADATA flag will be set
along with the data.

The mbuf dynamic field must be registered by calling
rte_flow_dynf_metadata_register() prior accessing the data.

The availability of dynamic mbuf metadata field can be checked with
rte_flow_dynf_metadata_avail() routine.

DEV_TX_OFFLOAD_MATCH_METADATA offload and configuration flag is removed.
The metadata support in PMDs is engaged on dynamic field registration.

Metadata feature is getting complex. We might have some set of actions
and items that might be supported by PMDs in multiple combinations,
the supported values and masks are the subjects to query by perfroming
trials (with rte_flow_validate).

[1] http://patches.dpdk.org/patch/62040/

Signed-off-by: Viacheslav Ovsiienko <viacheslavo@mellanox.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Olivier Matz <olivier.matz@6wind.com>
Acked-by: Ori Kam <orika@mellanox.com>