Fixes missing defintion OPENER_ETHLINK_INSTANCE_CNT

In MinGW and Windows versions this define is not found without include

Signed-off-by: Martin Melik Merkumians <melik-merkumians@acin.tuwien.ac.at>

source/src/cip/cipethernetlink.c

@@ -49,6 +49,7 @@
 #include "cipcommon.h"
 #include "opener_api.h"
 #include "trace.h"
+#include "opener_user_conf.h"
 
 #if OPENER_ETHLINK_INSTANCE_CNT > 1
   /* If we have more than 1 Ethernet Link instance then the interface label