msc: Fix Iu tests timing out due to explicit CM ServiceAccept not recvd

Even if ciphering it not enabled, osmo-msc still sends a
SecurityModeCommand to use IntegrityProtection, and as a result osmo-msc
assumes implicit ACCEPT in all UTRAN CM service requests.

Fixes: OS#3991
Change-Id: Ida91f907dd6dfae68cbc63752ddc6f2948792689
1 file changed