include: Switch to #pragma once pattern

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/gsm/rsl.h b/include/osmocom/gsm/rsl.h
index b8e4157..753dd19 100644
--- a/include/osmocom/gsm/rsl.h
+++ b/include/osmocom/gsm/rsl.h
@@ -1,5 +1,4 @@
-#ifndef _OSMOCORE_RSL_H
-#define _OSMOCORE_RSL_H
+#pragma once
 
 #include <stdint.h>
 #include <osmocom/core/utils.h>
@@ -51,5 +50,3 @@
 			    uint8_t link_id, int transparent);
 
 /*! @} */
-
-#endif /* _OSMOCORE_RSL_H */