allow a kernel argument to be passed through the reboot helper script, e.g.:

% reboot /sys/src/9/pc/9pccpu

Reference: /n/sources/patch/applied/rebootfull
Date: Wed Mar 30 23:25:15 CES 2005

--- /rc/bin/reboot	Wed Mar 30 23:24:32 2005
+++ /rc/bin/reboot	Wed Mar 30 23:24:30 2005
@@ -1,2 +1,2 @@
 #!/bin/rc
-echo reboot > /dev/reboot
+echo reboot $* > /dev/reboot