bridge: move mcast querier dumping code into a shared function

bridge: move mcast querier dumping code into a shared function

Put mcast querier dumping code into a shared function. This function
will be called from the bridge utility in a later patch.

Adapt the code such that the vtb parameter is used
instead of tb[IFLA_BR_MCAST_QUERIER_STATE].

Reviewed-by: Ido Schimmel <idosch@nvidia.com>
Acked-by: Nikolay Aleksandrov <razor@blackwall.org>
Signed-off-by: Fabian Pfitzner <f.pfitzner@pengutronix.de>
Signed-off-by: David Ahern <dsahern@kernel.org>