rc.subr: Fix premature return from wait_for_pids

Use pwait's new -r option to wait until the target processes have not
only terminated, but also been reaped.

PR:		293183
MFC after:	1 week
Sponsored by:	Klara, Inc.
Sponsored by:	NetApp, Inc.
Reviewed by:	markj
Differential Revision:	https://reviews.freebsd.org/D58391

UPDATING

@@ -27,6 +27,18 @@ NOTE TO PEOPLE WHO THINK THAT FreeBSD 16.x IS SLOW:
 	world, or to merely disable the most expensive debugging functionality
 	at runtime, run "ln -s 'abort:false,junk:false' /etc/malloc.conf".)
 
+20260722:
+	The wait_for_pids() function in rc.subr, used by rc scripts
+	when stopping or restarting a service, has been modified to
+	use pwait(1)'s new -r option, which requires kernel support.
+	When upgrading across this change, you should install a new
+	kernel first, then reboot, then install a new world, run
+	etcupdate, and reboot again.  Otherwise, you may find that
+	rc.subr is unable to stop services because the running kernel
+	does not provide the support that the updated pwait(1) needs.
+	Alternatively, if you deem it safe, you may use fastboot(8) to
+	reboot without shutting down services first.
+
 20260620:
 	On powerpc64le, long double is now IEEE 754 binary128 (quad
 	precision, 113-bit mantissa) instead of 64-bit double.  This is an