When sending a broadcast from a Linux bridge over a bridge port,
net/ipv4/ip_output.c::ip_dev_loopback_xmit() will send the packet back
to the bridge port. Currently, the bridge code will intercept this
loopback packet and try to bridge it. This is not right, the loopback
packet doesn't even have an Ethernet header. This loopback packet is
intended for the bridge port and should not be stolen by the bridge code.
The patch below fixes this by adding a check in __handle_bridge().
It also changes br_netfilter.c by only doing the paranoid checks of
br_nf_post_routing() when CONFIG_NETFILTER_DEBUG is set. I think the
loopback fix will get rid of any skbuffs matching those paranoid checks.

The patch also introduces/removes some whitespace in br_netfilter.c.