Merge remote-tracking branch 'origin/sysmocom/tbf-split'
the TBF handling in osmo-pcu mixes UL and DL TBFs together. They
are quite different, however, and should be treated differently.
This patch series continues the work of splitting up UL and DL TBFs
into their own classes and explicitly using a DL TBF or UL TBF
instead of the base class in those parts of the code that deal
with only one variant.
I didn't test every single commit, but each should compile and
the result passes make check as well as our iperf test against
a GSM modem.
[Text from Daniel's cover mail]