net: txgbe: add FDIR ATR support

Add flow director ATR filter. ATR mode is enabled by default to filter
TCP packets.

Signed-off-by: Jiawen Wu <jiawenwu@trustnetic.com>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: Paolo Abeni <pabeni@redhat.com>