debian: add patches for debian8

The osmocom-nightly/release can create debian8 package by patching
rules and control files

Change-Id: I261302d2ed16e76540073589504e7426e23d00a1
diff --git a/debian/patches/series b/debian/patches/series
new file mode 100644
index 0000000..82063b7
--- /dev/null
+++ b/debian/patches/series
@@ -0,0 +1 @@
+# build-for-debian8.patch