We used to set 'does_nr' of an UE if we detect ENDC supported in the
UE capabilities.

Then we activate NR measurements if 'does_nr' is true.

The problem is that if the eNB is not connected to a gNB but the UE
reports some NR measurements (because a gNB is running somewhere near)
then the eNB will crash when starting the switch to NR.

A (quick) solution is to set 'does_nr' only if there is a gNB connected to
the eNB.

Maybe not the best solution. To be changed if needed.