include: Switch to #pragma once pattern

Signed-off-by: Sylvain Munaut <tnt@246tNt.com>
diff --git a/include/osmocom/core/socket.h b/include/osmocom/core/socket.h
index cb1b7a8..1df28c9 100644
--- a/include/osmocom/core/socket.h
+++ b/include/osmocom/core/socket.h
@@ -1,5 +1,4 @@
-#ifndef _OSMOCORE_SOCKET_H
-#define _OSMOCORE_SOCKET_H
+#pragma once
 
 /*! \defgroup socket Socket convenience functions
  *  @{
@@ -37,5 +36,3 @@
 			    const char *socket_path, unsigned int flags);
 
 /*! @} */
-
-#endif /* _OSMOCORE_SOCKET_H */