arm: tegra12: enable netfilter ipv6/nat for tether

arm: tegra12: enable netfilter ipv6/nat for tether

Enable the following configs so as to enable 3G/4G tethering on T124.

IPv6 netfilter:
CONFIG_IP6_NF_IPTABLES
CONFIG_IP6_NF_FILTER
CONFIG_IP6_NF_TARGET_REJECT
CONFIG_IP6_NF_TARGET_REJECT_SKERR
CONFIG_IP6_NF_MANGLE
CONFIG_IP6_NF_RAW

NAT support for both IPv4:
CONFIG_NF_NAT_IPV4
CONFIG_IP_NF_TARGET_MASQUERADE
CONFIG_IP_NF_TARGET_NETMAP
CONFIG_IP_NF_TARGET_REDIRECT

Bug 1338421

Change-Id: Iceb501b8fb562503900cc82e7fa730c0e2fb15c4
Signed-off-by: Mark Kuo <mkuo@nvidia.com>
Reviewed-on: http://git-master/r/255321
Reviewed-by: Simone Willett <swillett@nvidia.com>
Tested-by: Simone Willett <swillett@nvidia.com>