Introduce tundev API

The data structre is held private so that it can be easily extended in
the future.

Change-Id: I6f8324da9ba49b9249682e2ec5b45297f18dd8c2
diff --git a/include/osmocom/core/Makefile.am b/include/osmocom/core/Makefile.am
index 3b2ef30..e1cd92a 100644
--- a/include/osmocom/core/Makefile.am
+++ b/include/osmocom/core/Makefile.am
@@ -55,6 +55,7 @@
 	thread.h \
 	timer.h \
 	timer_compat.h \
+	tun.h \
 	utils.h \
 	write_queue.h \
 	sockaddr_str.h \