libnetlink: add size argument to rtnl_talk

There have been several instances where response from kernel
has overrun the stack buffer from the caller. Avoid future problems
by passing a size argument.

Also drop the unused peer and group arguments to rtnl_talk.
diff --git a/ip/ipnetns.c b/ip/ipnetns.c
index 438d59b..be0c473 100644
--- a/ip/ipnetns.c
+++ b/ip/ipnetns.c
@@ -112,7 +112,7 @@
 		return fd;
 
 	addattr32(&req.n, 1024, NETNSA_FD, fd);
-	if (rtnl_talk(&rtnsh, &req.n, 0, 0, &answer.n) < 0) {
+	if (rtnl_talk(&rtnsh, &req.n, &answer.n, sizeof(answer)) < 0) {
 		close(fd);
 		return -2;
 	}
@@ -697,7 +697,7 @@
 
 	addattr32(&req.n, 1024, NETNSA_FD, fd);
 	addattr32(&req.n, 1024, NETNSA_NSID, nsid);
-	if (rtnl_talk(&rth, &req.n, 0, 0, NULL) < 0)
+	if (rtnl_talk(&rth, &req.n, NULL, 0) < 0)
 		err = -2;
 
 	close(fd);