Handle the case when TP-PI reserved bits are set

Discard settings according to 3GPP TS 23.040,
9.2.3.27 TP-Parameter-Indicator (TP-PI).

Usually operators will set this byte to 0 to indicate
there is no more data, but a few operators sets a
reserved bit to 1 to indicate there is no more data instead,
so we need to handle this case also.

Change-Id: I58abc2473c79b65795be186182927c603b35305e