nfd: Add nfd-dbg package with debug symbols of nfd and other binaries

Change-Id: Ic7b37f6527e4ff34418f31f09cc33b42086f3499
Refs: #11
diff --git a/nfd/debian/rules b/nfd/debian/rules
index 42884d3..ece0500 100755
--- a/nfd/debian/rules
+++ b/nfd/debian/rules
@@ -50,3 +50,7 @@
 	dh_systemd_start -pndn-autoconfig-server --no-start
 	dh_systemd_start -pndn-autoconfig-client --no-start
 	dh_systemd_start -pnfd-autoreg --no-start
+
+.PHONY: override_dh_strip
+override_dh_strip:
+	dh_strip --dbg-package=nfd-dbg