mgcp_client: add MGW name as logging context

Usually only one MGCP client per application is present. Then the log
lines from mgcp_client.c will be distinguishable without additional
information. When the application is using a pool of MGWs, then the
various MGCP Client instances become hard to distinguish.

- Add a possibility to set a description (name) for each MGW pool
  member. When no description is set, use the domain name.

- Output the pool member name on each log line in mgcp_client.c
  and mgcp_client_pool.c

Change-Id: I53ff5445c8e5faffa4ef908ffb1fdb1f47ea2904
Related: SYS#5091
6 files changed