bts: Fail OML in case the channel combination is wrong

In case a BTS is being bootstrapped and one TS can not be
activated prevent the whole BTS from coming up.

When the OML activation is not being done the rest of the BSC
code still assumes these logical channel(s) to be available
and one will see channel activation issues that might be hard
to debug.

Instead of having a half-configured system up and running,
keep the BTS offline.