net: dsa: bcm_sf2: Check earlier for FLOW_EXT and FLOW_MAC_EXT

We do not currently support matching on FLOW_EXT or FLOW_MAC_EXT, but we
were not checking for those bits being set in the flow specification.

The check for FLOW_EXT and FLOW_MAC_EXT are separated out because a
subsequent commit will add support for matching VLAN TCI which are
covered by FLOW_EXT.

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