Add sepolicy to lock down bpf access

Add a new set of sepolicy for the process that only netd use to load
and run ebpf programs. It is the only process that can load eBPF
programs into the kernel and is only used to do that. Add some
neverallow rules regarding which processes have access to bpf objects.

Test: program successfully loaded and pinned at sys/fs/bpf after device
boot. No selinux violation for bpfloader
Bug: 30950746

Change-Id: Ia6bb1afda29ae0749bdc368e2dfc5faa12e81b2f