drbd: Define the size of res_opts->cpu_mask in a single place

Signed-off-by: Andreas Gruenbacher <agruen@linbit.com>
Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
diff --git a/include/linux/drbd.h b/include/linux/drbd.h
index de7d74a..6f60136 100644
--- a/include/linux/drbd.h
+++ b/include/linux/drbd.h
@@ -382,4 +382,6 @@
 #define DRBD_MD_INDEX_FLEX_EXT -2
 #define DRBD_MD_INDEX_FLEX_INT -3
 
+#define DRBD_CPU_MASK_SIZE 32
+
 #endif