doc: update mgw settings in example config file

This example configuration files lack port settings for the mgcp
client. Lets explicitly assign a port for the MGW and a local port.
For the local port lets use the IETF port number + 1. The reason
for this is that the default config for osmo-bsc already uses the
IETF port and in osmo-bsc and osmo-msc run on the same machine in
many setups.

Change-Id: I17453e0d30eec757aba9530b63eb5d1539cbdffc

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

@@ -14,6 +14,8 @@ network
  mm info 1
 msc
  mgw remote-ip 10.23.24.1
+ mgw remote-port 2427
+ mgw local-port 2728
  assign-tmsi
  auth-tuple-max-reuse-count 3
  auth-tuple-reuse-on-error 1

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

@@ -22,4 +22,6 @@ msc
  cs7-instance-a 0
  cs7-instance-iu 0
  mgw remote-ip 10.23.24.1
+ mgw remote-port 2427
+ mgw local-port 2728
  assign-tmsi

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

@@ -24,4 +24,6 @@ msc
  cs7-instance-a 0
  cs7-instance-iu 1
  mgw remote-ip 10.23.24.1
+ mgw remote-port 2427
+ mgw local-port 2728
  assign-tmsi