deb: unbreak nightly builds

Add openbsc-dev with source and header files necessary for osmo-bts builds.

Max's note: extracted from Debian packaging work into separate commit.

Change-Id: I25f8c639d2dc525ca280a7cd09de3ca6358d2568
diff --git a/debian/openbsc-dev.install b/debian/openbsc-dev.install
new file mode 100644
index 0000000..557aea1
--- /dev/null
+++ b/debian/openbsc-dev.install
@@ -0,0 +1,2 @@
+openbsc/include/openbsc/gsm_data_shared.h usr/include/osmocom/openbsc/
+openbsc/src/libcommon/gsm_data_shared.c usr/src/osmocom/openbsc/libcommon/