This patch enables the use of IPv6 PDP contexts. The phone will
have to request an IPv6 End-user-Address, and the GGSN will have
to be configured for an IPv6 pool.
The outer transport-layer IP between SGSN and GGSN must still be
IPv4, it is not modified by this patch
Change-Id: I22c3bf32a98e5daf99d6eaeac8c9f95cc7574774