libmemif: add an include of sys/types.h header file

the ssize_t is defined there.

Change-Id: Ie46d196347ab91d0a92c15f331db14fe3b57061c
Type: fix
Signed-off-by: Andrew Yourtchenko <ayourtch@gmail.com>
diff --git a/extras/libmemif/src/libmemif.h b/extras/libmemif/src/libmemif.h
index 0146bb7..d1c5b05 100644
--- a/extras/libmemif/src/libmemif.h
+++ b/extras/libmemif/src/libmemif.h
@@ -28,6 +28,7 @@
 #define MEMIF_DEFAULT_APP_NAME "libmemif-app"
 
 #include <inttypes.h>
+#include <sys/types.h>
 #include <sys/timerfd.h>
 
 /*! Error codes */