dpif: Add support to set user features

dpif: Add support to set user features

This enables user features on the kernel datapath via the DP_CMD_SET
command, and also retrieves them to check for actual support and
not just an older kernel ignoring the requested features.

This will be used in next patch to enable recirc_id sharing with tc.

Signed-off-by: Paul Blakey <paulb@mellanox.com>
Reviewed-by: Roi Dayan <roid@mellanox.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>