sccp: Add Tests for SCMG SST procedure

The SST procedure can be used by any SCCP node to test the availability
of a remote SSN.  If the specified remote SSN is available at the
specified PC, a SCMG SSA is returned.  If not, there's a timeout.

Test for SSN=1 (SCMG), another non-SCMG SSN that exists, and for one
SSN that doesn't exist.

Change-Id: If3f5f3144c0ed83d0bda5953522a9d73287c8ba2
3 files changed