fix: fix pdu session modification crashing UPF

This merge request aims to fix the crash of the UPF when a PDU modification request is hold. Indeed, in case where a modification request with remove PDRs/FARs is sent to UPF, this latter should update accordingly the maps and remove far programs. In this fix: we have made the map has table entries to the deleted FARs and PDRs obsolete and have un-tailed the entry-point ebpf program from removed PDR/FAR program. These PDR/FAR programs are zambias within the kernel. Of course we still need to delete them, however at the time being, we don't have helper to delete them, so we need to implement that. Having them as zambias within the kernel is not a problem for now. maybe it will be an issue latter due to the max file descriptors allowed by the kernel.