Using a Bridge as a Gateway

If you want to use bridge as a gateway for other hosts you don't need to use the usual iptables nat, but you have to disable the iptableusage of the bridge altogether:

net.ipv4.ip_forward = 1

net.bridge.bridge-nf-call-ip6tables = 0
net.bridge.bridge-nf-call-iptables = 0
net.bridge.bridge-nf-call-arptables = 0