various: add %m in messages

Sometimes we want to suppress strerror() message because the are providing
something better. But in those cases, it seems it was just forgotten.

src/core/bpf-lsm.c

@@ -83,7 +83,7 @@ static int prepare_restrict_fs_bpf(struct restrict_fs_bpf **ret_obj) {
         r = restrict_fs_bpf__load(obj);
         assert(r <= 0);
         if (r < 0)
-                return log_error_errno(r, "Failed to load BPF object");
+                return log_error_errno(r, "Failed to load BPF object: %m");
 
         *ret_obj = TAKE_PTR(obj);
 

src/userdb/userwork.c

@@ -556,7 +556,7 @@ static int run(int argc, char *argv[]) {
                                         return log_error_errno(SYNTHETIC_ERRNO(EINVAL), "Parent already died?");
 
                                 if (kill(parent, SIGUSR2) < 0)
-                                        return log_error_errno(errno, "Failed to kill our own parent.");
+                                        return log_error_errno(errno, "Failed to kill our own parent: %m");
                         }
                 }
 

src/volatile-root/volatile-root.c

@@ -127,7 +127,7 @@ static int run(int argc, char *argv[]) {
 
         r = query_volatile_mode(&m);
         if (r < 0)
-                return log_error_errno(r, "Failed to determine volatile mode from kernel command line.");
+                return log_error_errno(r, "Failed to determine volatile mode from kernel command line: %m");
         if (r == 0 && argc >= 2) {
                 /* The kernel command line always wins. However if nothing was set there, the argument passed here wins instead. */
                 m = volatile_mode_from_string(argv[1]);