configs: Restore BRIDGE_NETFILTER=m

CONFIG_BRIDGE_NETFILTER=m used to be the default when CONFIG_NETFILTER
was enabled, but that was removed in 5.9. The way that defconfigs work
caused this wanted setting to be lost in rpi-5.9.y and rpi-5.10.y -
restore it now.

See: https://github.com/Hexxeh/rpi-firmware/issues/248



Signed-off-by: Phil Elwell <phil@raspberrypi.com>