Update GPRS attach according to 3GPP TS 24.008 version 12.8.0 Release…

[kheimerl]

Patch 9 PR. Some GPRS magic, not entirely sure what.

[kheimerl]

Hi @alexanderkjall , we're merging old orphaned openbts patches. Do you mind if we take yours?

Thanks!

[alexanderkjall]

I don't mind at all, but another user on the email list reported that this patch increased the error message rate in the log if I remember correctly. I think that there is more errors in the gprs stack that needs to be patched that this patch doesn't solve (something about the handling of P-TMSI's if I remember corretly, it was a long time since I looked at this).

[kheimerl]

Thanks for the info, we'll take a look.