nfp: flower: allow tunnels to output to internal port

The neighbour table in the FW only accepts next hop entries if the egress
port is an nfp repr. Modify this to allow the next hop to be an internal
port. This means that if a packet is to egress to that port, it will
recirculate back into the system with the internal port becoming its
ingress port.

Signed-off-by: John Hurley <john.hurley@netronome.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>