libgtp of the OpenGGSN project will allow us to speak the GTPv0/v1
protocol of the interface between SGSN and GGSN.
This commit includes code for the main libgtp integration (file
descriptor, select loop, timer) as well as code to encode/send
a CREATE PDP CONTEXT request.
We want the VTY and telnet code to be independent from the BSC
application(s). As a side note, we also like to eliminate static
global variables for 'struct gsm_network' all over the code.
As such, telnet_init() is now passed along a "private" pointer,
which getst stored in telnet_connection.priv. This telnet_connection
is then stored in vty->priv, which in turn gets dereferenced if
anyone needs a reference to 'struct gsm_network' from the BSC vty
code.
Also:
* vty_init() now calls cmd_init()
* the ugliness that telnet_init() calls back into the application by means of
bsc_vty_init() function has been removed.
* telnet_init() now returns any errors, so the main program can exit
e.g. if the port is already in use.
This enables us to make the VTY completely independent of any
compile-time program-specific information, i.e. one step closer
to using VTY as a shared library from multiple programs.