This patch implements a virtual physical layer replacing the air
interface. The purpose is to get rid of the hardware requirements
and be able to start testing and implementing layer 2 communication
functionality on one machine. Multicast sockets are used to enable
bidirectional communication between the BTS and the MS process.
The GSMTAP protocol designed for wireshark capturing is used to
encapsulate the payload on the virtual physical layer.
The virtual physical layer on the osmocom-bb side implements the
L1CTL interface to the layer23 apps like mobile.
* Working mcast socket communication and extraction of its
* Basic handlers for file descriptor callbacks from incoming L1CTL
messages and extraction of that functionality to a l1ctl socket class.
* Multiplexing to different routines depending on incoming L1CTL
* Uses virt_um and osmocom_mcast_sock implementation from osmo-bts
* Ecapsulation and parsing methods to and from GSMTAP messages.
* Basic handlers for file descriptor callbacks from incoming mcast
messages on the virtual um.
* Multiplexing to different channel routines based on GSMTAP header
* Example configuration for l23 app mobile using virtual test sim.