sip: test SDP forwarding via MNCC

Add CallPars.mncc_with_sdp: when true, the call establishing functions
f_establish_{mo,mt} now send valid SDP via MNCC, and validate that the
SDP received on MNCC and SIP are as expected.

Keep all current tests unchanged with mncc_with_sdp := false: they will
continue to test the case without SDP (for legacy compatibility). These
tests will still pass on the 'latest' builds.

Add two new tests for mncc_with_sdp := true: TC_mt_with_sdp and
TC_mo_with_sdp. These new tests will fail on our 'latest' builds until
the SDP forwarding feature in osmo-sip-connector is released.

Related: osmo-sip-connector I3df5d06f38ee2d122706a9ebffde7db4f2bd6bae
Change-Id: Ib2ae8449e673f5027f01d428d3718c006f76d93e
1 file changed