mgcp_client: use IETF source port as for MGCP

At the moment the mgcp client uses an arbitrary port as sourceport to
exchange MGCP messages with the MGW. However, IETF has designated a
specific port as sourceport for MGCP clients (Call agents), which is
2727. See also RFC3435, capter 3.5 Transmission over UDP.

- Change MGCP_CLIENT_LOCAL_PORT_DEFAULT from 0 to 2727

Change-Id: I96de84df3a3bf623d98b057ec3f3f621a3330a8a
Closes:	OS#2874
1 file changed