conn mode "sendonly" behaves identically to "sendrecv"
It's not anything we need at the moment, this is just to note down this factoid:
"sendonly" currently also happily receives.
How it happened: during testing of MGCP encoding, by random I sent an MDCX with conn mode = "sendonly";
I just set any conn mode that we use nowhere else to see whether the conn mode makes it to the MGCP encoding, which it did.
Then I was surprised to see that the voice call was still working fine despite all MGW endpoint CIs being set to "sendonly".