Some Serbian ISPs do not work.

[matijakljajic]

During testing for Fedora Silverblue on T14 and T14S (AMD editions) (Issue #206), we tried SIMs that are from different ISPs and 2 out of 3 seem to have problems. ISPs A1 and Yettel won't connect and keep displaying "Activation of network connection failed" error, while MTS, the state ISP, works but does appear to show the bug from (Issue #204) where signal shows very weak, 0%, but downloading and uploading works well.
Will update if I find a solution to A1 and Yettel problems.