msc: fix conn id in 'MGCP OK' msg (as_mgcp_ack_all_mdcx)

The MDCX OK message should contain the same connection identifier as the
MDCX contained. So far we were always sending the second conn id,
regardless of which conn id was sent in the MDCX message.

Related: SYS#5130
Change-Id: If6f7f135d95c04ee0240f3fa9ba0b18ffc6fa24a
1 file changed