nfp: allow control message reception on data queues

Port id 0xffffffff is reserved for control messages.  Allow reception
of messages with this id on data queues.  Hand off a raw buffer to
the higher layer code, without allocating SKB for max efficiency.
The RX handle can't modify or keep the buffer, after it returns
buffer is handed back over to the NIC RX free buffer list.

Signed-off-by: Jakub Kicinski <jakub.kicinski@netronome.com>
Reviewed-by: Dirk van der Merwe <dirk.vandermerwe@netronome.com>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>