GAtMux can now be made to work with multiple multiplexing protocols.
Currently on the 27.010 (07.10) Advanced and Basic modes are supported.
However, further protocol support can be added by providing the
necessary driver functions for GAtMux
ctx->server is never set to anything but 0. This was intended to handle
server side functionality of the GSM 07.10 multiplexer, but never fully
implemented. Since GAtMux is only really meant for the client side, we
can safely remove this dead code.