nfp flower action: Modified to use VLAN helper functions

Modified netronome nfp flower action to use VLAN helper functions instead
of accessing/referencing TC act_vlan private structures directly.

Reviewed-by: Pieter Jansen van Vuuren <pieter.jansenvanvuuren@netronome.com>
Signed-off-by: Manish Kurup <manish.kurup@verizon.com>
Signed-off-by: David S. Miller <davem@davemloft.net>