d/rules: reintroduce V=1

The iptables extensions/ makefile uses this variable to show verbose
information in the building proccess. I dropped this variable without checking
the results. It was there for a reason :-) Reintroduce it.
Signed-off-by: Arturo Borrero Gonzalez <arturo@debian.org>

debian/rules

@@ -2,6 +2,8 @@
 
 export DH_VERBOSE=1
 export DEB_BUILD_MAINT_OPTIONS = hardening=+all
+# used by iptables extensions/ makefile to be verbose:
+export V=1
 
 DEB_HOST_MULTIARCH ?= $(shell dpkg-architecture -qDEB_HOST_MULTIARCH)
 LIB_DIR := /usr/lib/$(DEB_HOST_MULTIARCH)