Fix AMF sends Registration Reject if 5GMM Capability IE was not provided by the UE

[abousselmi]

Hi,

The AMF is configured to set a registration reject if 5GMM Capability IE is not included. In some cases, for example with the OAI UE, the UE does not include this IE. I suggest we change the behavior to simply print a log warning and continue the registration procedure.

Please note that in case of OAI UE, the Registration procedure is successful with this change.

Closes #130

Thanks.

[andy89923]

Thanks for the PR;
I reword the commit message to comply with the conventional commit message.

[ianchen0119]

Hi @abousselmi

Thanks for your sharing!
However, the UE should indicate its 5GMM capability although this IE is optional.
For more information, please refer to the free5gc/free5gc#114.

Thanks again.

[abousselmi]

Thanks @ianchen0119

I think I should do the same and raise an issue on OAI side.

Closing this MR.