DIAMETER_Emulation: Notify user of CapabilityExchange

During start of the test case, we must wait until the IUT has
established a DIAMETER/SCTP connection to the testsuite.  Implement
this by means of a message on the DIAMETER_UNIT port and an associated
helper function.

Change-Id: I95434307efc67025ee6d373561f6d22398f959c5
2 files changed