msc_vlr_tests: add test_a5_3_not_supported

See also change-id I72a1dbb30e0a39dbf4b81c7e378d5607b62e10d3 in
osmo-ttcn3-hacks.git, which adds a similar test to the MSC_Tests.ttcn suite.

Writing this test helped me fix the issue faster, why not keep it now that it's
there.

Related: OS#2947
Change-Id: Iba56556207cf6e79e6531b0e7dd3eaec28fb5eaa
2 files changed