net/templates/osmo-sgsn.cfg: update format

Migrate to the new gprs_ns2_vty configuration introduced in osmo-sgsn
Ie9306ab4d4738c2c57a69987086e22771b30657e.

Change-Id: Ie0a6d4a55f725ebcc6a55b6bd71c52ad72accbd2

net/templates/osmo-sgsn.cfg

@@ -6,9 +6,9 @@ sgsn
  auth-policy remote
  gsup remote-ip ${HLR_IP}
 ns
- encapsulation udp local-ip ${SGSN_IP}
- encapsulation udp local-port ${SGSN_GB_PORT}
- encapsulation framerelay-gre enabled 0
+ bind udp local
+  listen ${SGSN_IP} ${SGSN_GB_PORT}
+  accept-ipaccess
 
 ${foreach(LOG_OUTPUT)}
 log ${LOG_OUTPUTn_TYPE}