genl: make string const

Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
diff --git a/genl/genl.c b/genl/genl.c
index 49b6596..e33fafd 100644
--- a/genl/genl.c
+++ b/genl/genl.c
@@ -54,7 +54,7 @@
 	return 0;
 }
 
-static struct genl_util *get_genl_kind(char *str)
+static struct genl_util *get_genl_kind(const char *str)
 {
 	void *dlh;
 	char buf[256];