doc: announce removal of ethdev flow director API
doc: announce removal of ethdev flow director API

The flow director config, part of the legacy filtering API,
was marked as deprecated last year.
A separate notice is added to make clear that these specific structs
will be removed as well in DPDK 20.11, as the rest of the legacy
filtering API.

Signed-off-by: Thomas Monjalon <5f50a84c1fa3bcff146405017f36aec1a10a9e38@monjalon.net>
Acked-by: Ajit Khaparde <01965fbd61169dc18f3fb5e13de7f67d298f8924@broadcom.com>
Acked-by: Jerin Jacob <352c4d4f9291b869992ddb67daa45ddc149fed30@marvell.com>
Acked-by: David Marchand <f28529695cfa9e3e1eb84e7072aa626af4abb18e@redhat.com>
Acked-by: Hemant Agrawal <90d96ef1ecd8ed49b97c7897be950e80824a9c5c@nxp.com>
Acked-by: Andrew Rybchenko <ac94ab2a8fe9a9a087f6e24dcbc16626b52c07e8@solarflare.com>

john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk,john-mcnamara-intel/dpdk