The code was changing the rnti in the red-black tree without
removing/reinserting the context. This is wrong because the
rnti is a key of the red-black tree and you cannot change the
key in a stored item at will.

There are also modifications of the function mac_eNB_rrc_ul_failure
which has to remove the UE in any case.

And rrc_mac_remove_ue has been changed for the case where
the UE is not found.

It creates more problems than it solves.

We replace this approach by a straightforward
synchronous one.

Now in the downlink, at frame f and subframe s
we use HARQ process (f * 10 + s) % 8.
This is similar to uplink scheduling.

The T has 2 processes: the tracee and the local tracer
if the tracee dies (segfault or whatever) the tracee
may still be running.

So there is a third process that monitors those two others
and kill everything when one dies.

The problem is that this third process has to be the parent
of the two others. That makes debugging the tracee with gdb
impossible. This new option disables the third monitor process.

Merge branch 'bugfix-96-Fix-build-script-for-16.04-installation-v3' of https://gitlab.eurecom.fr/oai/openairinterface5g into bugfix-96-Fix-build-script-for-16.04-installation-v3

we have to free memory in any case...

git status was way too noisy

libxslt1-dev is used at least for asn1 and usrp. It breaks the build when in
check_install_additional_tools().
Move it to to check_install_oai_software()