powerpc: Use default set of netfilter modules (CONFIG_NETFILTER_ADVANCED=n)

Our netfilter options are stale and important things like masquerading
are no longer enabled. Instead of trying to keep up with any updates,
set CONFIG_NETFILTER_ADVANCED=n on ppc64* and pseries* defconfigs.
This enables the most common netfilter modules for us.

While here, enable the network bridge module which is heavily used in
KVM setups.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>