core: suppress message about missing libbpf if in initrd()

It is quite likely that libbpf is not present in the initrd, and
there isn't much reason to use the bpf filters there.

https://bugzilla.redhat.com/show_bug.cgi?id=2084955#c25

src/core/bpf-util.c

@@ -26,7 +26,8 @@ bool cgroup_bpf_supported(void) {
 
         r = dlopen_bpf();
         if (r < 0) {
-                log_info_errno(r, "Failed to open libbpf, cgroup BPF features disabled: %m");
+                log_full_errno(in_initrd() ? LOG_DEBUG : LOG_INFO,
+                               r, "Failed to open libbpf, cgroup BPF features disabled: %m");
                 return (supported = false);
         }