doc: do not use random ip-address for MGW

The example configs suggest to use a random ip-address as MGW address.
Lets use a loopback address here. This will suit the usual case where
MGW and MSC run together on the same machine.

Change-Id: Ie2b2094fdcfed45353d9ba22cb07eed626fd143c

doc/examples/osmo-msc/osmo-msc.cfg

@@ -13,7 +13,7 @@ network
  rrlp mode none
  mm info 1
 msc
- mgw remote-ip 10.23.24.1
+ mgw remote-ip 127.0.0.1
  mgw remote-port 2427
  mgw local-port 2728
  assign-tmsi

doc/examples/osmo-msc/osmo-msc_custom-sccp.cfg

@@ -21,7 +21,7 @@ cs7 instance 0
 msc
  cs7-instance-a 0
  cs7-instance-iu 0
- mgw remote-ip 10.23.24.1
+ mgw remote-ip 127.0.0.1
  mgw remote-port 2427
  mgw local-port 2728
  assign-tmsi

doc/examples/osmo-msc/osmo-msc_multi-cs7.cfg

@@ -23,7 +23,7 @@ cs7 instance 1
 msc
  cs7-instance-a 0
  cs7-instance-iu 1
- mgw remote-ip 10.23.24.1
+ mgw remote-ip 127.0.0.1
  mgw remote-port 2427
  mgw local-port 2728
  assign-tmsi

tests/test_nodes.vty

@@ -160,7 +160,7 @@ msc
  auth-tuple-max-reuse-count 3
  auth-tuple-reuse-on-error 1
  mgw local-port 2728
- mgw remote-ip 10.23.24.1
+ mgw remote-ip 127.0.0.1
  mgw remote-port 2427
 mncc-int
  default-codec tch-f fr