Add OsmoGgsn class

Change-Id: I0eed70838e4e8656c4bc1337df70e631a10d69c7
diff --git a/src/osmo_gsm_tester/templates/osmo-ggsn.cfg.tmpl b/src/osmo_gsm_tester/templates/osmo-ggsn.cfg.tmpl
new file mode 100644
index 0000000..1ee19d1
--- /dev/null
+++ b/src/osmo_gsm_tester/templates/osmo-ggsn.cfg.tmpl
@@ -0,0 +1,74 @@
+!
+! OpenGGSN (0.94.1-adac) configuration saved from vty
+!!
+!
+log stderr
+  logging filter all 1
+  logging color 1
+  logging print category 1
+  logging print extended-timestamp 1
+  logging level ip info
+  logging level tun info
+  logging level ggsn info
+  logging level sgsn notice
+  logging level icmp6 notice
+  logging level lglobal notice
+  logging level llapd notice
+  logging level linp notice
+  logging level lmux notice
+  logging level lmi notice
+  logging level lmib notice
+  logging level lsms notice
+  logging level lctrl notice
+  logging level lgtp info
+  logging level lstats notice
+  logging level lgsup notice
+  logging level loap notice
+  logging level lss7 notice
+  logging level lsccp notice
+  logging level lsua notice
+  logging level lm3ua notice
+  logging level lmgcp notice
+  logging level all debug
+!
+stats interval 5
+!
+line vty
+ no login
+!
+ggsn ggsn0
+ gtp state-dir ${ggsn.statedir}
+ gtp bind-ip ${ggsn.ip_address.addr}
+ apn internet
+  gtpu-mode tun
+  tun-device tun4
+  type-support v4
+  ip prefix dynamic 176.16.222.0/24
+  ip dns 0 8.8.8.8
+  ip dns 1 8.8.8.4
+  ip ifconfig 176.16.222.1/24
+  no shutdown
+ apn inet6
+  gtpu-mode tun
+  tun-device tun6
+  type-support v6
+  ipv6 prefix dynamic fde4:8dba:82e1:2000:0:0:0:0/56
+  ipv6 dns 0 2001:4860:4860::8888
+  ipv6 dns 1 2001:4860:4860::8844
+  ipv6 ifconfig fde4:8dba:82e1:2000:0:0:0:0/56
+  no shutdown
+ apn inet46
+  gtpu-mode tun
+  tun-device tun46
+  type-support v4v6
+  ip prefix dynamic 176.16.46.0/24
+  ip dns 0 192.168.100.1
+  ip dns 1 8.8.8.8
+  ip ifconfig 176.16.46.0/24
+  ipv6 prefix dynamic fde4:8dba:82e1:2000:0:0:0:0/56
+  ipv6 dns 0 2001:4860:4860::8888
+  ipv6 dns 1 2001:4860:4860::8844
+  ipv6 ifconfig fde4:8dba:82e1:2000:0:0:0:0/56
+  no shutdown
+ default-apn internet
+ no shutdown ggsn