Fix sysctrl setup on boot

Add bridge module to /etc/modules to fix startap problem with
sysctl bridge parameters:

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

Related bug:
https://bugzilla.redhat.com/show_bug.cgi?id=634736