doc: announce ethdev API changes in offload flags

doc: announce ethdev API changes in offload flags

Add new offload flags ``DEV_RX_OFFLOAD_RSS_HASH`` and
``DEV_RX_OFFLOAD_FLOW_MARK``.
Add new function ``rte_eth_dev_set_supported_ptypes`` to allow application
to set specific ptypes to be updated in ``rte_mbuf::packet_type``

Signed-off-by: Pavan Nikhilesh <pbhagavatula@marvell.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>
Acked-by: Jerin Jacob <jerinj@marvell.com>
Acked-by: Hemant Agrawal <hemant.agrawal@nxp.com>
Acked-by: Konstantin Ananyev <konstantin.ananyev@intel.com>