This reverts commit b6513faa

This reverts commit 9efe4187

The discard timer is used by the PDCP layer to discard packets that were not
transmitted to RLC after some time.

We don't really need it for the moment, maybe never for the default
bearer which is a best-effort bearer passing all kind of IP traffic.
Maybe for voice over IP kind of traffic it's important, or realtime
applications.

I ran an iperf UDP uplink test and saw no error on the PHY layer but still
lots of packets lost in the iperf logs, which was very surprising. By
analyzing the logs in wireshark I saw that, with the current scheduler,
an IP packet sent by the UE took 40ms to be sent piece by piece to the
gNB, and then the next uplink IP packet was never sent at all because
the discard timer was expired, leading to the high count of packets lost
in the iperf logs.

So let's put infinity for the moment for the discard timer. From my
understanding of the moment it's not a problem. If for some reason we
should set it to some non-infinity value, then we can change later.

- FAPI structures not to be used as config_req at MAC since that FAPI is
  just for communication between MAC and PHY
- additional frame_type member added to the FAPI struct