ethdev: add isolated mode to flow API

ethdev: add isolated mode to flow API

Isolated mode can be requested by applications on individual ports to avoid
ingress traffic outside of the flow rules they define.

Besides making ingress more deterministic, it allows PMDs to safely reuse
resources otherwise assigned to handle the remaining traffic, such as
global RSS configuration settings, VLAN filters, MAC address entries,
legacy filter API rules and so on in order to expand the set of possible
flow rule types.

To minimize code complexity, PMDs implementing this mode may provide
partial (or even no) support for flow rules when not enabled (e.g. no
priorities, no RSS action). Applications written to use the flow API are
therefore encouraged to enable it.

Once effective, leaving isolated mode may not be possible depending on PMD
implementation.

Signed-off-by: Adrien Mazarguil <adrien.mazarguil@6wind.com>
Acked-by: Nelio Laranjeiro <nelio.laranjeiro@6wind.com>
Acked-by: Andrew Rybchenko <arybchenko@solarflare.com>