nfp: flower: add ipv6 bit to pre_tunnel control message

Differentiate between ipv4 and ipv6 flows when configuring the pre_tunnel
table to prevent them trampling each other in the table.

Fixes: 78346160 ("nfp: flower: update flow merge code to support IPv6 tunnels")
Signed-off-by: Louis Peens <louis.peens@corigine.com>
Signed-off-by: Simon Horman <simon.horman@netronome.com>
Signed-off-by: David S. Miller <davem@davemloft.net>