bugfix: don't force an UE to support en-dc, respect its capabilities

@melissa you introduced this some time ago. I don't think it's good. Are you okay with the change?

What happened for us is that a colleague of mine is trying to have FR2 NSA functional and he plays a lot with the settings of the UE. At some point, the UE was not endc capable anymore but we still saw in the logs of the enb that a second ue capabilities inquiry is done by the enb, but in the first ue capabilities there is no support for endc. Additionally, in the second message containing the ue capabilities reported by the UE, both nr and eutra-nr capabilities are empty, which was very surprising.

So I prefer that we ask for nr capabilities only if the UE reports a support for it.

I didn't touch the UE, only the enb.

(Actually we should do even more checks, like the band(s) reported by the UE. But the full logic of nsa is a bit primitive for the moment, so let's keep it simple as it is.)