Repair nFAPI in 5G

Add 5G nFAPI in OAI/Make it it work.

Many commits in this branch are basically bug fixes of things that don't work
properly, such as

- check for correct conditions (e.g. instance numbers in the RAN context)
- remove artificial limitation (e.g. only one PUCCH per TDD period in the PNF)
- improve performance (reduce big mallocs, make some static buffers such as a
  global ring buffer for nFAPI messages in the PNF)
- fix bugs in nFAPI (e.g., increase maximum message size to ~64kB instead of
  1500 bytes, because the latter is way too small for many TX_data.requests in
  5G, and it will delay message arrival unduly)
- fix bugs in message enc/dec (e.g., handle FDD in config.request)
- adjust the L1 such that the condition "we run monolithic" is not necessery
  (e.g., some message numbers in nFAPI struct where reset in MAC, instead of
  L1, and this breaks when running the PNF)

There are instructions that ...