session server BUGFIX missing header

Fixes #348
diff --git a/src/session_server.h b/src/session_server.h
index 532a181..1674ac7 100644
--- a/src/session_server.h
+++ b/src/session_server.h
@@ -22,6 +22,7 @@
 
 #include <libyang/libyang.h>
 #include <stdint.h>
+#include <sys/types.h>
 
 #ifdef NC_ENABLED_TLS
 # include <openssl/x509.h>