Add NULL check in the case of MNCC disconnect that was missing and
add an assert to show that at this point the other leg must exist.
Fixes: CID#80799, CID#80800, 80801
Initiate the setup request that should result in the call getting
all the way to the connected state at some point in time. The device
I test with sadly rejects the call too soon.
Fix releasing of the leg in case it is not routable and make the
differentation if we initiated the invite (send CANCEL) or send
a final error. The error code was randomly picked and once we have
an enum of causes we can decide where to map it to.
In case the MNCC server is crashing we need to release all calls,
use the event emitted by the MNCC connection and iterate over all
calls and call the release function.