net: dsa: bcm_sf2: Add support for IPv6 CFP rules

Inserting IPv6 CFP rules complicates the code a little bit in that we
need to insert two rules side by side and chain them to match a full
IPv6 tuple (src, dst IPv6 + port + protocol).

Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>