NS: Add support for persistent NS-VC configuration

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.
diff --git a/openbsc/src/gprs/osmo_gbproxy.cfg b/openbsc/src/gprs/osmo_gbproxy.cfg
index f2ef141..d51b04a 100644
--- a/openbsc/src/gprs/osmo_gbproxy.cfg
+++ b/openbsc/src/gprs/osmo_gbproxy.cfg
@@ -7,7 +7,7 @@
 !
 gbproxy
   nsip bss local port 23000
-  nsip sgsn remote ip 192.168.100.239
-  nsip sgsn remote port 23000
-  nsip sgsn nsei 1
-  nsip sgsn nsvci 11
+  nsip sgsn remote ip 127.0.0.1
+  nsip sgsn remote port 7777
+  nsip sgsn nsei 101
+  nsip sgsn nsvci 101