net/sfc: update comment about representor support

net/sfc: update comment about representor support

The representor support has been implemented to some extent, and the fact
that ethdev mport is equivalent to entity mport is by design.

Fixes: 1fb65e4dae8a ("net/sfc: support flow action port ID in transfer rules")
Cc: stable@dpdk.org
Signed-off-by: Viacheslav Galaktionov <viacheslav.galaktionov@oktetlabs.ru>
Signed-off-by: Andrew Rybchenko <andrew.rybchenko@oktetlabs.ru>
Reviewed-by: Andy Moreton <amoreton@xilinx.com>