5gc: Introduce test TC_connection_inactive
The test is expected to fail because open5gs (as of v2.7.3) doesn't
implement such features; see open5gs ticket referenced below.
Related: SYS#7073
Related: open5gs GH#4319
Change-Id: Icf60dde814b7c8ef4cdb4c886423058c7d741a9b
