Use reserved ip address for osmo-mgcpgw VTY interface

Otherwise 127.0.0.1 was being used and we want all interfaces for a
specific osmo-mgcpgw instance to use the same IP

Change-Id: I60dbfbb66458cd333fe07139ee175c94fa1672a7

src/osmo_gsm_tester/templates/osmo-mgcpgw.cfg.tmpl

@@ -5,6 +5,9 @@ log stderr
  logging print category 1
  logging print extended-timestamp 1
  logging level all debug
+line vty
+  no login
+  bind ${mgcpgw.ip_address.addr}
 mgcp
   local ip ${mgcpgw.ip_address.addr}
   bts ip ${mgcpgw.bts_ip}