Every NS-VC now has a set of counters for incoming and outgoing
number of packets and bytes.
We also split the VTY part of the gprs_ns.c implementation into gprs_ns_vty.c
to make sure the protocol can actually be used without the VTY code being
present.
With persistent NS-VC configuration (configured through VTY),
we can respond properly to BSS with a somewhat strange NS
implementation Such as the BSplus. It enables us to respond
with a proper NS-RESET (including NSVCI/NSEI) when receiving
a NS-ALIVE or other PDU for a BLOCKED/DEAD NS-VC after our
end of the connection is rebooted.
In order to reuse the existing bssgp_tx_* functions without pulling
in the dependencies of gprs_bssgp.c, we have to move those functions
to gprs_bssgp_util.c
Furthermore, we can remove gbprox_nsi and replace it with bssgp_nsi,
and we can do proper processing of BVC-RESET messages coming from
the SGSN on the signalling BVC. In that case we need to send RESET
messages to all the BSS.