There may be situations where we must check if there are still I.460
subchannels active, so lets make the function osmo_i460_subchan_count
public
Change-Id: I0454ffe5809f21504c1e263a781c06596d452d4b
Related: OS#5198
There are some parts of libosmogsm which are not really GSM specific,
but rather ISDN bits that were inherited by GSM. This includes the
I.460 multiplex as well as the core LAPD protocol.
Let's move those bits to its own libosmoisdn library, before we add
more ISDN specific bits to the wrong place.
Backwards-compatibility is created by making libosmogsm depend on
libosmoisdn, and by providing wrapper include files for source
compatibility.
Change-Id: Ib1a6c762322fd5047be3188b1df22408ef06aa50