When we send the RAB Assignment Request to the RNC, we need
to tell it the GGSN-side TEI for data, not "our" (SGSN side)
TEID.
In the RAB-Assignment.req we inform the RNC of the TEID on the GGSN
side, and in the RAB-Assignment.resp the RNC informs us of the TEID
on the RNC side.