dom0+vm/iptables: add PR-QBS-SERVICES chain in PREROUTING nat table

Additional chain for some qubes-related redirections. BTW PR-QBS should be
renamed now to PR-QBS-DNS...

network/iptables

@@ -4,7 +4,9 @@
 :OUTPUT ACCEPT [0:0]
 :POSTROUTING ACCEPT [0:0]
 :PR-QBS - [0:0]
+:PR-QBS-SERVICES - [0:0]
 -A PREROUTING -j PR-QBS
+-A PREROUTING -j PR-QBS-SERVICES
 -A POSTROUTING -o vif+ -j ACCEPT
 -A POSTROUTING -o lo -j ACCEPT
 -A POSTROUTING -j MASQUERADE