Cleanup GCC4 warnings about signedness.
diff --git a/lib/libnetlink.c b/lib/libnetlink.c
index 6ec2509..f7e8905 100644
--- a/lib/libnetlink.c
+++ b/lib/libnetlink.c
@@ -32,7 +32,7 @@
 
 int rtnl_open_byproto(struct rtnl_handle *rth, unsigned subscriptions, int protocol)
 {
-	int addr_len;
+	socklen_t addr_len;
 	int sndbuf = 32768;
 	int rcvbuf = 32768;