reactor: fix reserve_io_control_blocks config name in error message

adjust_max_networking_aio_io_control_blocks() logs a message when
it failed to allocate the desired amount of iocbs. This message mentions
the reserve_io_control_blocks by the incorrect name. Fix this.

Followup-fix for c5f9e3a.

Closes #2536

src/core/reactor.cc

@@ -4199,7 +4199,7 @@ unsigned smp::adjust_max_networking_aio_io_control_blocks(unsigned network_iocbs
                                      aio_nr + (requested_aio_other + smp::count), aio_nr + requested_aio);
 
             if (reserve_iocbs) {
-                err.append(format(", with an added reserve of {} (requested via io_control_blocks_reserve config)", reserve_iocbs));
+                err.append(format(", with an added reserve of {} (requested via reserve_io_control_blocks config)", reserve_iocbs));
             }
             unsigned smp_count_max = available_aio / (storage_iocbs + preempt_iocbs + 1);
             if (smp_count_max > 0) {