Update invirt-dhcp to version 0.0.11

Requested by mitchb/root@ATHENA.MIT.EDU

diff --git a/invirt-dhcp b/invirt-dhcp
index bffe12b..c7137ab 160000 (submodule)
--- a/invirt-dhcp
+++ b/invirt-dhcp
@@ -1 +1 @@
-Subproject commit bffe12b4fc25b1f66d48bcf3a1ad62e261c8fbb1
+Subproject commit c7137ab87b565e333d86ee161c1b54f5c9d8b187