osmo-mgw doesn't reject early bidirectional mode
It's illegal to activate a connection with "sendrecv" in the CRCX. The rationale is quite simple: if only the MGW-side port/ip information is known, how can there be bi-directional audio? osmo-mgw needs to reject this with error 527.
the osmo-ttcn3-hacks test case "TC_crcx_early_bidir_mode" tests this (and fails ever since it has been created in September).