Fix initial value of dom0 static-max entry

This value needs to be set to actual static max for qmemman to work
properly. If it's set higher than real static-max, qmemman will try to
assign more memory to dom0, which dom0 could not use - will be wasted.
Since this script is executed before any VM is started, simply
take the current dom0 memory usage, instead of parsing dom0_mem Xen
argument. There doesn't seem to be nice API to get this value from Xen
directly.

Fixes QubesOS/qubes-issues#4891

(cherry picked from commit 56ec271)

linux/aux-tools/startup-misc.sh

@@ -3,7 +3,7 @@
 # Misc dom0 startup setup
 
 /usr/lib/qubes/fix-dir-perms.sh
-DOM0_MAXMEM=`/usr/sbin/xl info | grep total_memory | awk '{ print $3 }'`
+DOM0_MAXMEM=$(/usr/sbin/xl list 0 | tail -1 | awk '{ print $3 }')
 xenstore-write /local/domain/0/memory/static-max $[ $DOM0_MAXMEM * 1024 ]
 
 xl sched-credit -d 0 -w 2000