bsc: Submit valid l3 payload

OsmoBSC does some minimal parsing of l3 content to select MSC target,
match paging response to paging request, etc.
Since tests right now use potentially invalid data, osmo-bsc is not
rejecting conns providing invalid l3 content.

This commit makes sure TTCN3 tests pass valid l3 payloads to osmo-bsc,
so that they keep working once osmo-bsc starts rejecting invalid IEs it
parses.

Related: SYS#6280
Change-Id: I6e99ac39f32c9a981420b73f8d7d1568d2fa1c54
3 files changed