android: configs: base: enable IPV6

android-base.cfg already enables several IPV6 sub-options, but not the
main IPV6 option.  Without this, build errors such has this:

   net/netfilter/xt_qtaguid.c:1591: undefined reference to `xt_socket_get6_sk'

occur if the starting defconfig hasn't already enabled IVP6,

Change-Id: I265089a2eec1ef8938e0a6fb95e1aacd16d99281
Cc: John Stultz <john.stultz@linaro.org>
Signed-off-by: Kevin Hilman <khilman@linaro.org>