mgcp_client: increment local port number when port is in use

The IETF has designated port 2727 for call agents (clients). This
works as long as only one call agent is running. As soon as two
call agents (e.g. osmo-bsc and osmo-msc) run on the same machine.
The port numbers will collide.

To avoid such a situation we will first try the IETF port and if
we fail to use it we increment the port number until we found a
usable port. However, we should only do this if the user has not
configured a non standard port. (The rationale behind this is that
if there is a non standard port configured the choice must have
been made conciously by the user and therefor we should fail hard
so that the user gets aware of the problem.)

Change-Id: Iaa5f41fdb43ec6bf4feaefa174fd82622e37d4d0
Related: OS#2874
1 file changed