increase rdroot size

ok kettenis@ deraadt@

src/etc/etc.armv7/disktab

@@ -1,10 +1,10 @@
-# $OpenBSD: disktab,v 1.6 2016/05/28 10:00:55 jsg Exp $
+# $OpenBSD: disktab,v 1.7 2020/04/03 23:18:36 jsg Exp $
 
 # Leave nc=16; adjust size using: ns
 rdroot|ramdiskroot|RAM-disk root FS image:\
-	:dt=rdroot:se#512:nc#16:nt#2:ns#480:\
-	:ta=4.2BSD:oa#0:pa#15360:fa#512:ba#4096:\
-	:ob#0:pb#0:oc#0:pc#15360:
+	:dt=rdroot:se#512:nc#16:nt#2:ns#496:\
+	:ta=4.2BSD:oa#0:pa#15872:fa#512:ba#4096:\
+	:ob#0:pb#0:oc#0:pc#15872:
 
 miniroot:\
 	:dt=rdroot:se#512:nc#9:nt#16:ns#256:\