tcap_as_loadshare: Fix compare ignoring non-TCAP messages and remove assert
The previous check in asp_loadshare_tcap_sccp() was was never true because it
checked msg class twice instead of class and type.
Also remove the OSMO_ASSERT in send_back_udts() limiting the function to
CL/DT messages.
Related: SYS#5432
Change-Id: I0831b289e4e4e94fd1b719e6c7164c3dd87c9f88
