libnetlink: __rtnl_talk_iov should only loop max iovlen times

William reported ip hanging and bisected to a recent commit for batching
allowing more than 1 command to be sent per message. The loop over
recvmsg should never cycle more than iovlen times -- 1 response for
each command in the message.

Fixes: 72a2ff3916 ("lib/libnetlink: Add a new function rtnl_talk_iov")
Signed-off-by: David Ahern <dsahern@gmail.com>

lib/libnetlink.c

@@ -670,8 +670,9 @@ next:
 						free(buf);
 					if (h->nlmsg_seq == seq)
 						return 0;
-					else
+					else if (i < iovlen)
 						goto next;
+					return 0;
 				}
 
 				if (rtnl->proto != NETLINK_SOCK_DIAG &&