bridge: Increase IGMP/MLD robustness parameter to three for br-client

We are mostly dealing with the 2.4GHz crap-band here, so increasing the
IGMP/MLD robustness parameter to three to be able to compensate for up
to two consecutive instead of just one lost packet.

Signed-off-by: Linus Lüssing <linus.luessing@c0d3.blue>