include: export lapd.h since openBSC needs it

More specifically, the unfinished ericsson rbs2000 BTS.
diff --git a/src/input/dahdi.c b/src/input/dahdi.c
index e7400e4..e411f9a 100644
--- a/src/input/dahdi.c
+++ b/src/input/dahdi.c
@@ -43,7 +43,7 @@
 #include <osmocom/abis/logging.h>
 #include <talloc.h>
 
-#include "lapd.h"
+#include <osmocom/abis/lapd.h>
 
 #define TS1_ALLOC_SIZE	300
 
diff --git a/src/input/lapd.c b/src/input/lapd.c
index 6c070e3..2e0dd08 100644
--- a/src/input/lapd.c
+++ b/src/input/lapd.c
@@ -36,7 +36,7 @@
 #include <assert.h>
 #include <errno.h>
 
-#include "lapd.h"
+#include <osmocom/abis/lapd.h>
 
 #include <osmocom/core/linuxlist.h>
 #include <osmocom/core/logging.h>