[LIBNFNETLINK] Fix wrong nfnetlink header size

Fix wrong size of the netfilter netlink header. This implicitely fixes an
alignment issue when nfnl_handle_packet is called as well.

Index: libnfnetlink/src/libnfnetlink.c
===================================================================
--- libnfnetlink.orig/src/libnfnetlink.c	2006-02-12 19:28:19.000000000 +0100
+++ libnfnetlink/src/libnfnetlink.c	2006-02-12 19:30:00.000000000 +0100
@@ -914,7 +914,7 @@ int nfnl_check_attributes(const struct n
 	if (type >= ssh->cb_count)
 		return -EINVAL;
 
-	min_len = NLMSG_ALIGN(sizeof(struct nfgenmsg));
+	min_len = NLMSG_SPACE(sizeof(struct nfgenmsg));
 	if (nlh->nlmsg_len < min_len)
 		return -EINVAL;
 #endif