L1CTL: Add support for CCCH_MODE_COMBINED_CBCH

In OsmocomBB/trxcon Change-Id Ia94ebf22a2ec439dfe1f31d703b832ae57b48ef2
we introduced a new mode CCCH_MODE_COMBINED_CBCH to indicate that the
channel combination is a CCCH+SDCCH/4 with one SDCCH stolen for CBCH.

Let's make sure we actually use that mode in our CBCH related tests

Change-Id: I27ee2c81bec7175c1ea09d4f3f6037f2866fe242
3 files changed