net: bridge: constify variables in the replay helpers

Some of the arguments and local variables for the newly added switchdev
replay helpers can be const, so let's make them so.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>