Update invirt-dhcp to version 0.0.12

Requested by mitchb/root@ATHENA.MIT.EDU

diff --git a/invirt-dhcp b/invirt-dhcp
index c7137ab..149df32 160000 (submodule)
--- a/invirt-dhcp
+++ b/invirt-dhcp
@@ -1 +1 @@
-Subproject commit c7137ab87b565e333d86ee161c1b54f5c9d8b187
+Subproject commit 149df324e6f1aca5ba2f043dba6614c65b499968