mi_startup: Instrument the bubblesort with TSLOG

The bubblesort of SYSINITs is currently responsible for 7% of the
kernel boot time when booting a 1 CPU / 128 MB VM under Firecracker.

It needs to be replaced with a faster sort, but until that happens
at least instrumenting it with TSLOG makes it show up in flamecharts.

sys/kern/init_main.c

@@ -255,6 +255,7 @@ restart:
 	 * Perform a bubble sort of the system initialization objects by
 	 * their subsystem (primary key) and order (secondary key).
 	 */
+	TSENTER2("bubblesort");
 	for (sipp = sysinit; sipp < sysinit_end; sipp++) {
 		for (xipp = sipp + 1; xipp < sysinit_end; xipp++) {
 			if ((*sipp)->subsystem < (*xipp)->subsystem ||
@@ -266,6 +267,7 @@ restart:
 			*xipp = save;
 		}
 	}
+	TSEXIT2("bubblesort");
 
 	last = SI_SUB_COPYRIGHT;
 #if defined(VERBOSE_SYSINIT)