pid1: lower log level if BPF LSM is not available

Currently, if you boot PID 1 in a container you always see a complaint
that BPF LSM won't work. That's fine, and log worthy, but probably not
above debug level. After all this is a really common case, and we should
gracefully adopt to our execution environment.

src/core/bpf-restrict-fs.c

@@ -107,7 +107,7 @@ bool bpf_restrict_fs_supported(bool initialize) {
 
         r = lsm_supported("bpf");
         if (r == -ENOPKG) {
-                log_info_errno(r, "bpf-restrict-fs: securityfs not mounted, BPF LSM support not available.");
+                log_debug_errno(r, "bpf-restrict-fs: securityfs not mounted, BPF LSM support not available.");
                 return (supported = false);
         }
         if (r < 0) {