stp: Introduce STP_Tests_TCAP
The network topology and test infrastructure already allows testing TCAP forwarding
at STP over IPA<->IPA, M3UA<->IPA and M3UA<->M3UA.
Co-authored-by: Alexander Couzens <lynxis@fe80.eu>
Related: SYS#5423
Change-Id: I4340bdf126118c66af861f5a447e90883783920e
